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  • Saccharomyces cerevisiae
  • stability
  • Springer  (61)
  • 1990-1994  (61)
  • 1955-1959
  • 1991  (61)
Collection
Publisher
Years
  • 1990-1994  (61)
  • 1955-1959
Year
  • 1
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    Acta biotheoretica 39 (1991), S. 1-14 
    ISSN: 1572-8358
    Keywords: Hematological diseases ; first order partial differential equations ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To address the possibility that proliferative disorders may originate from interactions between multiple populations of proliferating and maturing cells, we formulate a model for this process as a set of coupled nonlinear first order partial differential equations. Using recent results for the asymptotic behaviour of the solutions to this model, we demonstrate that there exists a region of coupling coefficients, maturation rates, and proliferation rates that will guarantee the stable coexistence of coupled cellular populations. The analysis shows that increases in the coupling between populations may ultimately lead to a loss of stability. Furthermore, the analysis indicates that increases (decreases) in the maturation and/or proliferation rates above (below) critical levels will lead either to instability in the populations or the destruction of one population and the persistence of the other.
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  • 2
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    Catalysis letters 10 (1991), S. 225-232 
    ISSN: 1572-879X
    Keywords: VPI-5 ; stability ; molecular sieve ; post-synthesis treatments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thorough washing of a VPI-5 synthesized with n-dipropylamine as template improves greatly its thermal stability while no major change is observed in the template content. A detailed study of the influence of the pretreatment conditions shows that in order to obtain a high thermal stability (up to at least 960 °C) two parameters are of importance. The removal of both the template and the adsorbed water requires either a low heating rate at atmospheric pressure or a low pressure (less than 3 Torr) when the heating rate is 300 ° per hour.
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  • 3
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    Journal of industrial microbiology and biotechnology 7 (1991), S. 131-135 
    ISSN: 1476-5535
    Keywords: Saccharomyces cerevisiae ; Jerusalem artichoke ; High-fructose syrup ; Ethanol ; Immobilized yeast cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The results from this study showed that Jerusalem artichoke juice can be used for the production of very enriched fructose syrup by selective conversion of glucose to ethanol in a continuous process using immobilized cells ofSaccharomyces cerevisiae ATCC 36859. The product contained up to 99% of the total carbohydrates as fructose compared to 76% in the feed. Using Jerusalem artichoke juice supplemented with some glucose a product was obtained with 7.5% w/v ethanol which made ethanol recovery economically favourable. It was found that some fructose was consumed in these continuous processes; the glucose/fructose conversion rate ratio was regulated by the glucose concentration in the product stream.
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  • 4
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    Journal of industrial microbiology and biotechnology 7 (1991), S. 181-189 
    ISSN: 1476-5535
    Keywords: Saccharomyces cerevisiae ; Torulaspora delbrueckii ; Aroma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Thirty-three fermentations of Pedro Ximénez grapes, collected in three degrees of ripeness, were carried out by inoculation with three types of inoculum: pure cultures ofSaccharomyces cerevisiae races and ofTorulaspora delbrueckii, indigenous yeasts, and mixed cultures of indigenous yeasts enriched with the pure cultures. By means of variance analysis 21 compounds were determined whose final concentrations in the wines significantly depended on the musts, the inocula or both. Eleven products that depended significantly on the inocula were subjected to a discriminant analysis in which most of the pure cultures gathered in a discriminant space area different from that occupied by the indigenous yeasts. The centroids corresponding to most of the mixed cultures were shifted to the central area of the discriminant space, moved away from their corresponding pure cultures and approached the indigenous yeasts. The results show a high similarity between the fermentations carried out with mixed cultures with the addedS. cerevisiae races and those fermentations carried out with the indigenous yeasts, with regard to those compounds which were significantly dependent on the inocula.
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  • 5
    ISSN: 1432-0983
    Keywords: Schizosaccharomyces pombe ; Saccharomyces cerevisiae ; Argininosuccinate lyase ; Sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The complete nucleotide sequence of the ARG7 gene, coding for argininosuccinate lyase (EC 4.3.2.1), in the fission yeast (Schizosaccharomyces pombe) has been determined. It consists of an open reading frame of 461 codons. The deduced protein has a molecular weight of 51 200 Da. The gene is devoid of introns which is confirmed by the fact that it is expressed in Escherichia coli after spontaneous insertion of a bacterial sequence probably bearing a prokaryotic promoter. A perfect “TATA” box is found at-72 and the major transcription initiation site in Saccharomyces cerevisiae is located at-11 as shown by primer extension experiments. Comparison of the S. pombe lyase with related proteins from other organisms reveals an important degree of conservation except in the carboxyterminal part of the polypeptide. Additionally, a deletion removing 66 amino acids of the carboxy terminus yields an enzyme exhibiting some biological activity. A unique 1500 b transcript was found in S. cerevisiae when the intact gene was present, but the deleted version of the gene gave rise to at least three transcripts of 1800, 2800 and 3900 b.
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  • 6
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Pyrimidine salvage pathway ; Semi-dominant mutants ; FUR1 ; Uracil phosphoribosyl transferase ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Saccharomyces cerevisiae, the protein encoded by the FUR1 gene is absolutely required for the expression of uracil phosphoribosyl transferase activity. The occurrence of semi-dominant mutations for 5-fluorouracil-(5FU)-resistance at this locus led us to clone and sequence the semi-dominant fur 1–5 allele. A single point mutation, resulting in the substitution of arginine 134 for serine, is responsible for this mutant phenotype. The fur 1–5 allele is transcribed and expressed at the same level as the wild-type allele. But, in contrast with the wild-type, the UPR Tase activity of the fur 1–5 mutant strain is stimulated in vitro by UTP and does not, therefore, correspond to a loss of feedback of UPR Tase activity. We found that uracil, as a free base, induces a significative increase in transcription and UPR Tase activity in a wild-type strain as well as in uracil-overproducing mutants which principally explains the high efficiency of the pyrimidine salvage pathway in S. cerevisiae.
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  • 7
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Centromere flanking sequences ; tRNA modification enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Transcriptional analysis of the region flanking the left boundary of the centromere of chromosome VI revealed the presence of a gene immediately adjacent to CEN6. The transcription of the gene is directed toward the centromere, and nucleotide sequence analysis showed that the coding region terminates only 50 bp away from CEN6. Our results extend to chromosome VI the observation that centromere-flanking regions of S. cerevisiae are transcriptionally active. Disruption of the coding region of the gene showed that its product, whilst not essential for cell viability, is important for normal cell growth. The gene has been termed DEG1 (DEpressed Growth rate). Comparison of the deduced amino acid sequence of DEG1 with a protein sequence databank revealed homology with the enzyme tRNA pseudouridine synthase I of E. coli.
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  • 8
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    Current genetics 19 (1991), S. 9-14 
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Mevalonate kinase ; Ergosterol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nucleotide sequence of the ERG12 gene, encoding mevalonate kinase, from Saccharomyces cerevisiae is presented. The longest open reading frame may code for a protein containing 443 amino acids with a deduced relative molecular mass of 48 500. The analysis of the nucleotide sequence reveals a complete identity with the yeast gene RAR1, isolated elsewhere by complementation of a rar1 mutation involved in the stability of plasmids with weak ARS. In addition, we show that mevalonate kinase is not a rate-limiting enzyme; however its sensitivity to FFP could be a key regulatory mechanism in the sterol pathway of yeast.
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  • 9
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    Microchimica acta 104 (1991), S. 467-482 
    ISSN: 1436-5073
    Keywords: prediction ; stability ; multivariate methods ; graphical analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sizeable data bases are now being routinely generated in a variety of contexts in chemical industry. Statistical investigations of such data bases are aimed both at initially uncovering structure and eventually proposing models, in particular for predicting product quality by the mix or characteristics of the chemical compounds. “Online Multivariate Exploratory Graphical Analysis” (OMEGA) stands for a structured exploratory study of the relationships in a multivariate data set, where, rather than testing for one specific property, as many clues as possible for interesting structures are searched for by different dimension reductions and succeeding interactive graphical analyses. The stability of the projections obtained by the different dimension reduction methods is assessed by simulation producing graphical displays particularly supporting the identification of influential points. The variation of the predictions obtained by the different dimension reduction methods is assessed by cross-validation delivering misclassification rates or cross-validated R2 values. The interpretation of the new coordinates corresponding to dimension reduction is supported by loading simplifications and graphical displays for judging its adequacy. The OMEGA strategy has been found to be an effective tool for routine searching for structure.
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  • 10
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    K-Theory 4 (1991), S. 363-397 
    ISSN: 1573-0514
    Keywords: Nonabelian K 1 ; noncommutative homotopy ; general linear group ; superspecial linear groups ; descending central series ; stability ; relative normal subgroups ; nilpotent sandwich classifications ; quasi-finite algebras
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A functorial filtration GL n =S−1L n $$ \supseteq$$ S0L n $$ \supseteq$$ ⋯ $$ \supseteq$$ S i L n $$ \supseteq$$ ⋯ $$ \supseteq$$ E n of the general linear group GL n, n ⩾ 3, is defined and it is shown for any algebra A, which is a direct limit of module finite algebras, that S−1 L n (A)/S0L n (A) is abelian, that S0L n (A) $$ \supseteq$$ S1L n (A) $$ \supseteq$$ ⋯ is a descending central series, and that S i L n (A) = E n(A) whenever i ⩾ the Bass-Serre dimension of A. In particular, the K-functors k 1 S i L n =S i L n /E n are nilpotent for all i ⩾ 0 over algebras of finite Bass-Serre dimension. Furthermore, without dimension assumptions, the canonical homomorphism S i L n (A)/S i+1 L n (A)→S i L n+ 1(A)/S i+1 L n + 1 (A) is injective whenever n ⩾ i + 3, so that one has stability results without stability conditions, and if A is commutative then S0L n (A) agrees with the special linear group SL n (A), so that the functor S0L n generalizes the functor SL n to noncommutative rings. Applying the above to subgroups H of GL n (A), which are normalized by E n(A), one obtains that each is contained in a sandwich GL′ n (A, ρ) $$ \supseteq$$ H $$ \supseteq$$ E n(A, ρ) for a unique two-sided ideal ρ of A and there is a descending S0L n (A)-central series GL′ n (A, ρ) $$ \supseteq$$ S0L n (A, ρ) $$ \supseteq$$ S1L n (A, ρ) $$ \supseteq$$ ⋯ $$ \supseteq$$ S i L n (A, ρ) $$ \supseteq$$ ⋯ $$ \supseteq$$ E n(A, ρ) such that S i L n (A, ρ)=E n(A, ρ) whenever i ⩾ Bass-Serre dimension of A.
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  • 11
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    Current genetics 20 (1991), S. 167-171 
    ISSN: 1432-0983
    Keywords: Glycolysis ; Repetitive elements τ/δ ; Promoter ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In this study we report on the complete nucleotide sequence of the yeast phosphoglycerate mutase gene (GPM1) and its essential 5′ and 3′ non-coding regions. The transcriptional start points were determined by S1-mapping and sequencing of a cDNA clone. Several sequences identified as important for transcriptional regulation in yeast promoters are present upstream of the transcription start point. 3′ to the coding region we sequenced a composite repetitive element which, apparently, originated from a recombination between a delta-and a tau-element. Finally, we mapped the GPM1 gene 13 cM distal to fas1 on chomosome XI.
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  • 12
    ISSN: 1432-0789
    Keywords: Antifungal activity ; Saccharomyces cerevisiae ; Phytopathogenic fungi ; Heterocyclic non-protein amino acid ; Pisum sativum ; Constitutive plant defence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary β-(Isoxazolin-5-on-2-yl)-alanine (βIA), a heterocyclic non-protein amino acid from root extracts and root exudates of pea seedlings, acts as a potent growth inhibitor of several eukaryotic organisms, including yeasts, phytopathogenic fungi, unicellular green algae, and higher plants. The antibiotic effect on baker's yeast was reversed by l-methionine, l-cysteine, and l-homocysteine. Phytopathogenic fungi such as Botrytis cinerea, Pythium ultimum, and Rhizoctonia solani grown on agar containing βIA were inhibited in the growth of mycelia or in the production of sclerotia. In contrast, no significant inhibition of either Gram-positive or Gram-negative bacteria was observed. Rhizobium leguminosarum, the compatible microsymbiont of Pisum spp., and Rhizobium meliloti were able to tolerate up to 2.9 mM βIA (500 ppm) without any effect on the growth rate. Bradyrhizobium japonicum even gave a positive chemotactic response to βIA. The ecological significance of βIA as a preformed plant protectant during the seedling stage of Pisum spp. and other βIA-containing legumes is discussed.
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  • 13
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    Current genetics 20 (1991), S. 189-194 
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Bakers' and lager yeast ; Chromosomal and 2 μm DNA polymorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seven strains of bakers' yeast were obtained as a representative sample of the Spanish baking industry. The nuclear genome was monitored for polymorphism by transverse alternating field electrophoresis (TAFE) and restriction maps of 2 μm DNA were produced. All seven strains were uniquely different when evaluated by their total chromosomal lengths whereas only two 2 μm variants were defined. There was no apparent correlation between chromosomal and plasmid polymorphism. The extensive chromosomal polymorphism within one 2 μm DNA type indicates the rapid and relatively recent evolution of the nuclear genome. The hybrid origin (S. cerevisiae-S.monacensis) of lager yeast was critically evaluated by TAFE analysis of S. cerevisiae and S. carlsbergensis chromosomes. The absence of corresponding S. cerevisiae chromosomes III and XIII in S. carlsbergensis argued against the hybrid origin of lager strains. We discuss limitations of the hybrid origin hypothesis of industrial yeasts and propose that the molecular coevolution observed in 2 μm DNA serves as a useful additional mechanism for rationalization of some of the structural polymorphism of the nuclear genome.
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  • 14
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    Current genetics 20 (1991), S. 437-439 
    ISSN: 1432-0983
    Keywords: Schizosaccharomyces pombe ; Saccharomyces cerevisiae ; β-glucuronidase ; Colony colour assay ; Fluorometric assay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Expression of the β-galactosidase gene in yeast has served as a screening marker for many purposes. Here it is shown that in two yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, the β-glucuronidase (GUS) gene can be used as an alternative marker. Since the histochemical substrate can not be taken up by yeast cells, direct colony screening of plates was found to be impossible. However, by a replica plating technique, GUS expression became visibly detectable within 10 min when the GUS gene was strongly expressed. The staining method could still be performed for expression at a 100-fold lower level, but incubation times of several hours were needed. Furthermore, specific GUS expression levels of yeast protein extracts could be quantified by a fluorometric assay which is both very simple to perform and highly sensitive. Since the GUS gene can also tolerate large N-terminal fusions, this method should be particularly attractive for studying such diverse problems as transcriptional and translational regulation or subcellular localization in yeast.
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  • 15
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    Current genetics 20 (1991), S. 181-184 
    ISSN: 1432-0983
    Keywords: Alpha amylase ; Secretion ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Extracellular glucoamylase activity was increased by a gene, which is present in super-secretor, but absent in low-secretor, strains of the yeast Saccharomyces cerevisiae. Genetic data indicated that this super-secretor gene is linked to the STA3 structural gene for glucoamylase. This gene appears to act specifically since it increased the secretion of glucoamylase but not of other secreted enzymes like acid phosphatase and invertase.
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  • 16
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Melibiose fermentation ; MEL ; Polymeric genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We used a combination of genetic hybridization analysis and electrokaryotyping with radioactively labelled MEL1 gene probe hybridization to isolate and identify seven polymeric genes for the fermentation of melibiose in strain CBS 5378 of Saccharomyces cerevisiae (syn. norbensis). Four of the MEL genes, i.e. MEL3, MEL4, MEL6 and MEL7, were allelic to those found in S. cerevisiae strain CBS 4411 (syn. S. oleaginosus) whereas three genes, i.e. MEL8, MEL9 and MEL10 occupied new loci. Electrokaryotyping showed that all seven MEL genes in CBS 5378 were located on different chromosomes. The new MEL8, MEL9 and MEL10 genes were found on chromosomes XV, X/XIV and XII, respectively.
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  • 17
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Ergosterol ; Squalene synthetase ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ERG9 gene of Saccharomyces cerevisiae has been cloned by complementation of the erg9-1 mutation which affects squalene synthetase. From the 5kkb insert isolated, the functional gene has been localized on a DNA fragment of 2.5 kb. The presence of squalene synthetase activity in E. coli bearing the yeast DNA fragment isolated, indicates that the structural gene encoding squalene synthetase has been cloned. The sequence of the 2.5 kb fragment contains an open reading frame which could encode a protein of 444 amino acids with a deduced relative molecular mass of 51 600. The amino acid sequence reveals one to four potential transmembrane domains with a hydrophobic segment in the C-terminal region. The N-terminus of the deduced protein strongly resembles the signal sequence of yeast invertase suggesting a specific mechanism of integration into the membranes of the endoplasmic reticulum.
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  • 18
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; β-phenethyl-alcohol ; ARO4 gene ; DAHP synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary o-Fluoro-dl-phenylalanine (OFP)-resistant mutants which overproduce β-phenethyl-alcohol were isolated from a laboratory strain of Saccharomyces cerevisiae. Cells of one of the mutants accumulated tyrosine and phenylalanine 1.5–3 fold more than did wild-type cells. Its 3-deoxy-d-arabino-hepturosonate-7-phosphate (DAHP) synthase (EC 4.1.2.15), encoded by ARO4, was free from feedback inhibition by tyrosine. Genetic analysis revealed that the mutation was controlled by a single dominant gene, ARO4-OFP, encoding feedback-resistant DAHP synthase by tyrosine, and that this gene caused both the OFP resistance and β-phenethyl-alcohol overproduction. This was supported by molecular genetic studies using cloned ARO4 both from the wild-type and its mutant strain.
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  • 19
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    Journal of nonlinear science 1 (1991), S. 289-311 
    ISSN: 1432-1467
    Keywords: cytogel ; mechanochemical ; two-dimensional patterns ; cellular differentiation ; pattern formation ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary Contractile actomyosin systems play a central role in the generation of intracellular patterns. Models for pattern formation have benefited greatly from the application of mechanochemical theory. However, investigations of the patterns have been primarily qualitative in nature; the two-dimensional nature of the evolving patterns has not yet been addressed mathematically, nor has the evolution of stable heterogeneous steady-state solutions. We consider these issues, supporting our analytical predictions with numerical simulations in one and two spatial dimensions. We show how, for certain gels, the two and three-dimensional tensor equation which describes a balance of forces can be reduced to a reaction-diffusion equation.
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  • 20
    ISSN: 1432-072X
    Keywords: Candida tropicalis ; Saccharomyces cerevisiae ; Peroxisomes ; Isocitrate lyase ; GAL7 promoter ; High level expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genomic DNA of peroxisomal isocitrate lyase (ICL) isolated from an n-alkane-assimilating yeast, Candida tropicalis, was truncated to utilize the original open reading frame under the control of the GAL7 promoter and was expressed in Saccharomyces cerevisiae. The recombinant ICL was synthesized as a functionally active enzyme with a specific activity similar to the enzyme purified from C. tropicalis, and was accounted for approximately 30% of the total extractable proteins in the yeast cells. This recombinant enzyme was easily purified to homogeneity. N-Terminal amino acid sequence, molecular masses of native form and subunit, amino acid composition, peptide maps, and kinetic parameters of the recombinant ICL were essentially the same as those of ICL purified from C. tropicalis. From these facts, S. cerevisiae was suggested to be an excellent microorganism to highly express the genes encoding peroxisomal proteins of C. tropicalis.
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  • 21
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    Archives of microbiology 156 (1991), S. 38-42 
    ISSN: 1432-072X
    Keywords: Water stress ; Saccharomyces cerevisiae ; Glycerol ; Yeast water relations ; Osmoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When exponentially growing Saccharomyces cerevisiae was transferred from a normal high water activity growth medium (aw 0.997) to a medium containing 8% NaCl low water activity growth medium (aw 0.955), glycerol accumulation during the first eight hours of the adaptation was both retarded and greatly diminished in magnitude. Investigation of the underlying reasons for the slow onset of glycerol accumulation revealed that not only was overall glycerol production reduced by salt transfer, but also the rates of ethanol production and glucose consumption were reduced. Measurement of glycolytic intermediates revealed an accumulation of glucose-6-phosphate, fructose-6-phosphate, fructose 1,6 bisphosphate and phosphoenolpyruvate in S. cerevisiae 3 to 4 h after transfer to salt, suggesting that one or more glycolytic enzymes were inhibited. Potassium ions accumulated in S. cerevisiae after salt transfer and reached a maximum about 6 h after transfer, whereas the sodium ion content increased progressively during the adaptation period. The trehalose content also increased in adapting cells. It is suggested that inhibition of glycerol production during the initial period of adaptation could be due to either the inhibition of glycerol-3-phosphate dehydrogenase by increased cation content or the inhibitin of glycolysis, glycerol being produced glycolytically in S. cerevisiae. The increased accumulation of glycerol towards the end of the 8-h period suggests that the osmoregulatory response of S. cerevisiae involves complex sets of adjustments in which inhibition of glycerol-3-phosphate dehydrogenase must be relieved before glycerol functions as a major osmoregulator.
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  • 22
    ISSN: 1573-4919
    Keywords: glutathione reductase ; Saccharomyces cerevisiae ; redox interconversion ; metals ; cell-free extracts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Redox inactivation of glutathione reductase involves metal cations, since chelators protected against NADPH-inactivation, 3 µM EDTA or 10 µM DETAPAC yielding full protection. Ag+, Zn2+ and Cd2+ potentiated the redox inactivation promoted by NADPH alone, while Cr3+, Fe2+, Fe3+, Cu+, and Cu2+ protected the enzyme. The Zn2+ and Cd2+ effect was time-dependent, unlike conventional inhibition. Glutathione reductase interconversion did not require dioxygen, excluding participation of active oxygen species produced by NADPH and metal cations. One Zn2+ ion was required per enzyme subunit to yield full NADPH-inactivation, the enzyme being reactivated by EDTA. Redox inactivation of glutathione reductase could arise from the blocking of the dithiol formed at the active site of the reduced enzyme by metal cations, like Zn2+ or Cd2+. The glutathione reductase activity of yeast cell-free extracts was rapidly inactivated by low NADPH or moderate NADH concentrations; NADP+ also promoted rapid inactivation in fresh extracts, probably after reduction to NADPH. Full inactivation was obtained in cell-free extracts incubated with glucose-6-phosphate or 6-phosphogluconate; the inactivating efficiency of several oxidizable substrates was directly proportional to the specific activities of the corresponding dehydrogenases, confirming that redox inactivation derives from NADPH formed in vitro.
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  • 23
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    Applied mathematics and mechanics 12 (1991), S. 1017-1021 
    ISSN: 1573-2754
    Keywords: predator ; prey ; patch ; population ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper we study the stability for equilibrium points of equations in two-population dynamics. We discuss two predator-prey-patch models. Model 1 is described by a differential equation. Model 2 is described by an integral differential equation. We obtain the conditions for the stability of their equilibrium points. The results show that the overall population stability despite local extinction is realizable.
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  • 24
    ISSN: 1573-2754
    Keywords: stability ; nonautonomous system ; frequently-acting perturbation ; state transition matrix ; robot
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The necessary and sufficient condition of the stability of linear nonautonomous system under the frequently-acting perturbation has been given and proved on the basis of [1] and [2], and the theorem of the equivalence on the uniform and asymptotical stability in the sense of Liapunov and the stability under the frequently-acting perturbation of linear nonautonomous system has been given in this paper. Besides, the analysis of the dynamic stability of robot has been presented by applying the theorem in this paper, which is closer to reality.
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  • 25
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    Applied mathematics and mechanics 12 (1991), S. 539-545 
    ISSN: 1573-2754
    Keywords: fluid flow ; stability ; unsteady ; plane Poiseuille flow ; multiple scale method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper investigates the linear stability behaviour of plane Poiseuille flow under unsteady distortion by multiscale perturbation method and discusses further the problem proposed by paper [1]. The results show that in the initial period of disturbance development, the distortion profiles presented by paper [1] will make the disturbances grow up, thus augmenting the possibility of instability.
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  • 26
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    Applied mathematics and mechanics 12 (1991), S. 415-420 
    ISSN: 1573-2754
    Keywords: bending ; flexural function ; stability ; vibration ; critical force ; frequency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract For the bending, stability and vibrations of rectangular thin plates with free edges on elastic foundations, in this paper we give a flexural function which exactly satisfies not only all the boundary conditions on free edges but also the conditions at free corner points. Applying energy variation principle, we give equations defining parameters in flexural function, stability equation, frequency equation, and general formulae of minimum critical force and minimum eigenfrequency as well.
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  • 27
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    Applied mathematics and mechanics 12 (1991), S. 1001-1008 
    ISSN: 1573-2754
    Keywords: stability ; initial value problem ; differentiability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, using the differentiability of the solution with respect to the initial value and the parameter, we present a method which, different from Liapunov's direct method, will determine the stability of the non-stationary solution of the initial value problem when the non-stationary solution remains unknown.
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  • 28
    ISSN: 1573-4943
    Keywords: Screening protein structures ; electroblotting ; glucose-6-phosphate dehydrogenase ; Saccharomyces cerevisiae ; Pichia jadinii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Rapid assessment of structural relationships between yeast glucose-6-phosphate dehydrogenases and other eukaryotic types of this enzyme is described. Separation and size estimation of large fragments by sodium dodecylsulfate/polyacrylamide gel electrophoresis, electroblotting onto disks, and sequencer analysis provide data that permit alignment of the segments thus characterized with the related proteins, and utilize existing structural knowledge to assess new enzyme structures. Affinity labeling allows further correlations. The results establish the overall structural arrangements of the new proteins, including the location of the active-site lysine residue, even though the yeast enzyme structures are found to differ markedly from the few previously characterized glucose-6-phosphate dehydrogenases.
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  • 29
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    Molecular genetics and genomics 230 (1991), S. 241-250 
    ISSN: 1617-4623
    Keywords: Yeast ; Saccharomyces cerevisiae ; Adenylyl cyclase ; CDC25 ; RAS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The TFS1 gene of Saccharomyces cerevisiae is a dosage-dependent suppressor of cdc25 mutations. Overexpression of TFS1 does not alleviate defects of temperature-sensitive adenylyl cyclase (cdc35) or ras2 disruption mutations. The ability of TFS1 to suppress cdc25 is allele specific: the temperature-sensitive cdc25-1 mutation is suppressed efficiently but the cdc25-5 mutation and two disruption mutations are only partially suppressed. TFS1 maps to a previously undefined locus on chromosome XII between RDN1 and CDC42. The DNA sequence of TFS1 contains a single long open reading frame encoding a 219 amino acid polypeptide that is similar in sequence to two mammalian brain proteins. Insertion and deletion mutations in TFS1 are haploviable, indicating that TFS1 is not essential for growth.
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  • 30
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    Molecular genetics and genomics 226 (1991), S. 224-232 
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; SAM1 and SAM2 genes ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary S-adenosyl-l-methionine (AdoMet) is synthesized by transfer of the adenosyl moiety of ATP to the sulfur atom of methionine. This reaction is catalysed by AdoMet synthetase. In all eukaryotic organisms studied so far, multiple forms of AdoMet synthetases have been reported and from their recent study, it appears that AdoMet synthetase is an exceptionally well conserved enzyme through evolution. In Saccharomyces cerevisiae, we have demonstrated the existence of two AdoMet synthetases encoded by genes SAM1 and SAM2. Yeast, which is able to concentrate exogenously added AdoMet, is thus a particularly useful biological system to understand the role and the physiological significance of the preservation of two almost identical AdoMet synthetases. The analysis of the expression of the two SAM genes in different genetic backgrounds during growth under different conditions shows that the expression of SAM1 and SAM2 is regulated differently. The regulation of SAM1 expression is identical to that of other genes implicated in AdoMet metabolism, where as SAM2 shows a specific pattern of regulation. A careful analysis of the expression of the two genes and of the variations in the methionine and AdoMet intracellular pools during the growth of different strains lead us to postulate the existence of two different AdoMet pools, each one suppplied by a different AdoMet synthetase but in equilibrium with each other. This could be a means of storing AdoMet whenever this metabolite is overproduced, thus avoiding the degradation of a metabolite the synthesis of which is energetically expensive.
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  • 31
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Calmodulin-binding protein ; Protein phosphatase (2B type) ; Calcineurin A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Saccharomyces cerevisiae genomic clones that encode calmodulin-binding proteins were isolated by screening a λgt11 expression library using125I-labeled calmodulin as probe. Among the cloned yeast genes, we found two closely related genes (CMP1 andCMP2) that encode proteins homologous to the catalytic subunit of phosphoprotein phosphatase. The presumed CMP1 protein (62999 Da) and CMP2 protein (68496 Da) contain a 23 amino acid sequence very similar to those identified as calmodulin-binding sites in many calmodulin-regulated proteins. The yeast genes encode proteins especially homologous to the catalytic subunit of mammalian phosphoprotein phosphatase type 213 (calcineurin). The products of theCMP1 andCMP2 genes were identified by immunoblot analysis of cell extracts as proteins of 62000 and 64000 Da, respectively. Gene disruption experiments demonstrated that elimination of either or both of these genes had no effect on cell viability, indicating that these genes are not essential for normal cell growth.
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  • 32
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; recA gene expression ; Resistance to ionizing and ultraviolet radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Escherichia coli recA protein coding region was ligated into an extrachromosomally replicating yeast expression vector downstream of the yeast alcohol dehydrogenase promoter region to produce plasmid pADHrecA. Transformation of the wild-type yeast strains YNN-27 and 7799-4B, as well as the recombination-deficient rad52-t C5-6 mutant, with this shuttle plasmid resulted in the expression of the bacterial 38 kDa RecA protein in exponential phase cells. The wild-type YNN27 and 7799-4B transformants expressing the bacterial recA gene showed increased resistance to the toxic effects of both ionizing and ultraviolet radiation. RecA moderately stimulated the UV-induced mutagenic response of 7799-4B cells. Transformation of the rad52-t mutant with plasmid pADHrecA did not result in the complementation of sensitivity to ionizing radiation. Thus, the RecA protein endows the yeast cells with additional activities, which were shown to be error-prone and dependent on the RAD52 gene.
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  • 33
    ISSN: 1617-4623
    Keywords: Fungi ; Saccharomyces cerevisiae ; Zinc ; Processing ; Pro region
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The neutral protease II (NpII) from Aspergillus oryzae is a zinc-containing metalloprotease with some unique properties. To elucidate its structure, we isolated a full-length cDNA clone for NpII. Sequence analysis reveals that NpII has a prepro region consisting of 175 amino acids preceding the mature region, which consists of 177 amino acids. As compared with other microbial metalloproteases, NpII is found to be unique in that it shares only a limited homology with them around two zinc ligand His residues and that the positions of the other zinc ligand (Glu) and the active site (His) cannot be established by homology. When a plasmid designed to express the prepro NpII cDNA was introduced into Saccharomyces cerevisiae and the transformant was cultured in YPD medium (2% glucose, 2% polypeptone, 1% yeast extract), it secreted a proNpII. However, in a culture of the same medium containing 0.2 mM ZnCl2, it secreted a mature NpII with a specific activity and N-terminus identical to those of native NpII. This observation suggests that either an autoproteolytic activity or a yeast protease effected the processing.
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  • 34
    ISSN: 1617-4623
    Keywords: Ricin ; Toxin ; Mutant ; Saccharomyces cerevisiae ; Expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Yeast transformants containing integrated copies of a galactose-regulated, ricin toxin A chain (RTA) expression plasmid were constructed and used in an attempt to isolate RTA-resistant yeast mutants. Analysis of RNA from mutant strains demonstrated that approximately half contained ribosomes that had been partially modified by RTA, although all the strains analysed transcribed full-length RTA RNA. The mutant strains could have mutations in yeast genes giving rise to RTA-resistant ribosomes or they could contain alterations within the RTA-encoding DNA causing production of mutant toxin. Ribosomes isolated from mutant strains were shown to be susceptible to RTA modification in vitro suggesting that the strains contain alterations in RTA. This paper describes the detailed analysis of one mutant strain which has a point mutation that changes serine 203 to asparagine in RTA protein. Although serine 203 lies outside the proposed active site of RTA its alteration leads to the production of RTA protein with a greatly reduced level of ribosome modifying activity. This decrease in activity apparently allows yeast cells to survive expression of RTA as only a proportion of the ribosomes become modified. We demonstrate that the mutant RTA preferentially modifies 26S rRNA in free 60S subunits and has lower catalytic activity compared with native RTA when produced in Escherichia coli. Such mutations provide a valuable means of identifying residues important in RTA catalysis and of further understanding the precise mechanism of action of RTA.
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  • 35
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; CTP synthetase ; Pyrimidine pathway ; Intracellular pyrimidine pool ; Non-essential gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The URA7 gene of Saccharomyces cerevisiae encodes CTP synthetase (EC 6.3.4.2) which catalyses the conversion of uridine 5′-triphosphate to cytidine 5′-triphosphate, the last step of the pyrimidine biosynthetic pathway. We have cloned and sequenced the URA 7 gene. The coding region is 1710 by long and the deduced protein sequence shows a strong degree of homology with bacterial and human CTP synthetases. Gene disruption shows that URA7 is not an essential gene: the level of the intracellular CTP pool is roughly the same in the deleted and the wild-type strains, suggesting that an alternative pathway for CTP synthesis exists in yeast. This could involve either a divergent duplicated gene or a different route beginning with the amination of uridine mono- or diphosphate.
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  • 36
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Lysyl-tRNA synthetase ; PMR2 repeat ; Genome organization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary TheKRS1 gene encodes the cytoplasmic form ofSaccharomyces cerevisiae lysyl-tRNA synthetase. TheKRS1 locus has been characterized. The lysyl-tRNA synthetase gene is unique in the yeast genome. The gene is located on the right arm of chromosome IV and disruption of the open reading frame leads to lethality. These results contrast with the situation encountered inEscherichia coli where lysyl-tRNA synthetase is coded by two distinct genes,lysS andlysU, and further address the possible biological significance of this gene duplication. The nucleotide sequence of the 3′-flanking region has been established. It encodes a long open reading frame whose nucleotide and amino acid structures are almost identical toPMR2, a cluster of tandemly repeated genes coding for P-type ion pumps. The sequence alterations relative toPMR2 are mainly located at the C-terminus of the protein.
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  • 37
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; mRNA metabolism ; Nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutations in the PRP20 gene of yeast show a pleiotropic phenotype, in which both mRNA metabolism and nuclear structure are affected. srm1 mutants, defective in the same gene, influence the signal transduction pathway for the pheromone response. The yeast PRP20/SRM1 protein is highly homologous to the RCC1 protein of man, hamster and frog. In mammalian cells, this protein is a negative regulator for initiation of chromosome condensation. We report the analysis of two, independently isolated, recessive temperature-sensitive prp20 mutants. They have identical G to A transitions, leading to the alteration of a highly conserved glycine residue to glutamic acid. By immunofluorescence microscopy the PRP20 protein was localized in the nucleus. Expression of the RCC1 protein can complement the temperature-sensitive phenotype of prp20 mutants, demonstrating the functional similarity of the yeast and mammalian proteins.
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  • 38
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    Molecular genetics and genomics 228 (1991), S. 335-344 
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; DNA interstrand cross-links ; DNA repair ; Electron microscopy
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    Topics: Biology
    Notes: Summary The repair of interstrand cross-links induced by 8-methoxypsoralen plus UVA (365 nm) radiation DNA was analyzed in diploid strains of the yeast Saccharomyces cerevisiae. The strains employed were the wild-type D7 and derivatives homozygous for the rad18-1 or the rad3-12 mutation. Alkaline step-elution and electron microscopy were performed to follow the process of induction and removal of photoinduced crosslinks. In accordance with previous reports, the D7 rad3-12 strain failed to remove the induced lesions and could not incise cross-links. The strain D7 rad18-1 was nearly as efficient in the removal of 8-MOP photoadducts after 2 h of post-treatment incubation as the D7 RAD+ wild-type strain. However, as demonstrated by alkaline step-elution and electron microscopic analysis, the first incision step at DNA cross-links was three times more effective in D7 rad18-1 than in D7 RAD+. This is consistent with the hypothesis that the RAD18 gene product is involved in the filling of gaps resulting from persistent non-informational DNA lesions generated by the endonucleolytic processing of DNA cross-links. Absence of this gene product may lead to extensive strand breakage and decreased recognition of such lesions by structural repair systems.
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  • 39
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Ty ; Transcriptional activation ; SPT13/GAL11 ; SPT14
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To investigate the role of the trans-acting transcription factor encoded by the essential SPT14 (SPT=Suppressor of Ty insertion mutations) gene, we have cloned, mapped and sequenced the gene. From the analysis of the effect of spt14 mutations on expression of various genes, we conclude that the SPT14 product has an important role in activation of Ty transcription as well as in the regulation of other genes including HIS4 and several of the a- and α-specific mating type genes. Similarities in the phenotypes of spt14 and spt13 mutants (suppression of Ty insertion mutations but not δ insertion mutations), lead to the suggestion that the SPT14 gene and the previously characterized SPT13/GAL11 gene might encode transcriptional regulators with related functions. Our current findings show that in contrast to SPT13/GAL11, which appears negatively to regulate Ty transcription, SPT14 plays a role in the activation of Ty transcription. Thus, despite the similarities in the suppression phenotype exhibited by spt13 and spt14 mutants, SPT13/GAL11 and SPT14 probably differ in their transcriptional roles.
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  • 40
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Splicing ; prp mutants ; Linker insertion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the yeast Saccharomyces cerevisiae, some thermosensitive (ts) mutants have been shown to be impaired in pre-mRNA splicing (prp mutants). From a yeast genomic library, we have isolated plasmids that complement prp6 or prp9 is mutations. These plasmids also complement the is growth defect of additional independent mutants identified as new prp6 and prp9 is alleles, indicating that the cloned DNAs encode PRP6 and PRP9 genes, respectively. Here, we describe the restriction maps of these loci which are localized on chromosome II and IV, respectively. The limits of open reading frames (ORFs) within the cloned inserts have been determined using a linker insertion strategy combined with the is complementation assay. Double-strand DNA sequencing was also performed directly on the yeast expression vector from the inserted linkers. Gene disruption experiments demonstrate that both genes are essential for viability.
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  • 41
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; TRPI promoter ; Upstream activating sequences ; PGK
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The interactions between different upstream activator sequences (UAS) and the downstream transcriptional elements of the TRP1 promoter were studied. We have inserted the UAS from the PGK gene into a series of TRP1 promoter deletions such that the PGK UAS is positioned at various distances upstream from or replaces the TRP1 UAS (UAST1). We show that activation of the TRP1 transcription unit I by the PGK UAS shows a marked position dependence, which is solely a function of the position of the PGK UAS relative to sequences involved in the determination of the RNA initiation sites in the TRP1 promoter. No cooperative activation is seen when both UASs are present in the promoter; the PGK UAS is dominant and is not repressed by the TRPI negative element. In addition, we show that the PGK and TRP1 UASs interact differently with TATA sequence at the TRP1 RNA initiation site. Our results suggest that these UASs are functionally distinct because they use different mechanisms for activating heterologous promoters.
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  • 42
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    Molecular genetics and genomics 225 (1991), S. 340-341 
    ISSN: 1617-4623
    Keywords: Intron ; Group I ; DNA endonuclease ; Mitochondria ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two group I intron-encoded proteins from the yeast mitochondrial genome have already been shown to have a specific DNA endonuclease activity. This activity mediates intron insertion by cleaving the DNA sequence corresponding to the splice junction of an intronless strain. We have discovered in mitochondrial extracts from the yeast strain 777-3A a new DNA endonuclease activity which cleaves the fused exon A3-exon A4 junction sequence of the COXI gene.
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  • 43
    ISSN: 1617-4623
    Keywords: RNase H ; Salmonella typhimurium ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have cloned genes encoding RNase H from Escherichia coli rnh mutants, Salmonella typhimurium and Saccharomyces cerevisiae. Selection was accomplished by suppression of the temperature-sensitive growth phenotype of Escherichia coli strains containing the rnh-339::cat and either recB270 (Ts) or recC271 (Ts) mutations. RNases H from E. coli and S. typhimurium contained 155 amino acid residues and differed at only 11 positions. The S. cerevisiae and E. coli RNases H were about 30% homologous. A comparison of the amino acid sequences of several RNases H from cellular and retroviral sources revealed some strongly conserved regions as well as variable regions; the carboxyl-terminus was particularly variable. The overlapping, divergent promoter gene organization found in E. coli was observed to be present in S. typhimurium.
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  • 44
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    Molecular genetics and genomics 227 (1991), S. 452-457 
    ISSN: 1617-4623
    Keywords: CDC7 ; Saccharomyces cerevisiae ; Protein kinase ; Cell cycle ; DNA synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The product of the CDC7 gene of Saccharomyces cerevisiae has multiple cellular functions, being needed for the initiation of DNA synthesis during mitosis as well as for synaptonemal complex formation and commitment to recombination during meiosis. The CDC7 protein has protein kinase activity and contains the conserved residues characteristic of the protein kinase catalytic domain. To determine which of the cellular functions of CDC7 require this protein kinase activity, we have mutated some of the conserved residues within the CDC7 catalytic domain and have examined the ability of the mutant proteins to support mitosis and meiosis. The results indicate that the protein kinase activity of the CDC7 gene product is essential for its function in both mitosis and meiosis and that this activity is potentially regulated by phosphorylation of the CDC7 protein.
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  • 45
    ISSN: 1573-5060
    Keywords: Analytical breeding ; barley ; drought resistance ; landraces ; Hordeum vulgare ; stability ; stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Attempts to identify individual traits to use as an indirect measure for grain yield have shown some degree of success in environments where crop yields are affected by no stress or only by predictable stresses. However, analytical breeding has been largely unsuccessful in the case of a) stressful environments characterized by low yields due to high variability in the frequency, timing, duration and severity of a number of climatic stresses, and b) breeding programs where the major objective is greater yield stability defined as a reduction in the frequency of crop failures. Experimental evidence suggests that, when environmental variability is high due to unpredictable differences in frequency, timing and severity of various climatic stresses, each time different combinations of several traits are likely to confer ‘drought resistance’. Interaction among traits in determining overall crop response to variable stresses is expected to occasionally enhance the importance of a specific trait in a specific stress situation. In this context it becomes difficult to consider ‘drought resistance’ as a character with its own identity in terms of inheritance. Assessment and verification of traits based on the use of isogenic lines tends to oversimplify the interactions between traits, as the approach provides information on the effect of a specific trait only in a specific genetic background. At the population level of organisation, the dilemma between selection for individual traits and specific combinations of traits can be translated into the dilemma between selection for individual genotypes and specific combinations of genotypes. The evidence that natural selection under stress conditions has not been able to identify either a single trait or a single genotype with a given ‘adapted’ architecture of traits, is discussed in relation to germplasm development philosophies to stabilize yield in unpredictably stressed environments.
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  • 46
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    Transport in porous media 6 (1991), S. 281-298 
    ISSN: 1573-1634
    Keywords: Seasonal heat storage ; heat transport ; unsaturated soils ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We present a model of heat and mass transfer in an unsaturated zone of sand and silty clay soils, taking into account the effects of temperature gradients on the advective flux, and of the enhancement of thermal conduction by the process of latent heat transfer through vapor flow. The motivation for this study is to supply information for the planned storage of thermal energy in unsaturated soils and for hot waste storage. Information is required on the possibility of significant drying at a hot boundary, as this would reduce the thermal conductivity of a layer adjacent to the boundary and, thus, prevent effective heat transfer to the soil. This study indicates the possibility that the considered system may be unstable, with respect to the drying conditions, with the occurrence of drying depending on the initial and the boundary conditions. An analysis performed for certain boundary conditions of heat transfer and for given soil properties, disregarding the advective flux of energy, indicated that there are initial conditions of water content for which heating will not cause significant drying. Under these conditions, fine soils may be better suited for heat transfer at the hot boundary, due to their higher field capacity, although their heat conduction coefficients at saturation are lower than those of sandy soils. At present, these conclusions are limited to the range of 50–80°C. Potential effects of solute concentration at the hot boundary are indicated.
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  • 47
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    Antonie van Leeuwenhoek 59 (1991), S. 269-283 
    ISSN: 1572-9699
    Keywords: growth physiology ; plasmid stability ; recombinant cell culture ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Despite the fact that plasmid stability in the yeastSaccharomyces cerevisiae is influenced by both genetical and physiological parameters most attention has been focussed on the former. Physiological factors affecting the stability of plasmids have been poorly characterized despite the need for such information in order to optimize the use ofS. cerevisiae as a host for recombinant protein production processes. The physiology of wild typeS. cerevisiae differs considerably when grown using different cultivation techniques. A limited amount of phenomenological data has been reported concerning plasmid instability effects under these different conditions and in this article these have been collected together with the intention of providing an overview to instability effects and to try and propose reasons as to how the physiological response to different growth conditions can be manifested as stability/instability effects.
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    Journal of statistical physics 65 (1991), S. 725-745 
    ISSN: 1572-9613
    Keywords: Aggregation ; injection ; power law distribution ; stability ; relaxation ; stable distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study a generalized aggregation process in which charged particles diffuse and coalesce randomly on a lattice. For one-dimensional and mean-field models, we show that there exists a statistically-invariant steady state when randomly charged particles are continuously injected. The steady-state charge distribution obeys a power law with the exponent depending both on the type of the injection and on the spatial dimension. The response of the system to a perturbation (i.e., relaxation) is characterized by either a power law decay (t −β ,β⩽1) or a compressed exponential decay [exp(−t α ),α〉1].
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  • 49
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    Euphytica 57 (1991), S. 157-167 
    ISSN: 1573-5060
    Keywords: Hordeum vulgare ; barley ; stability ; subsistence agriculture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Groups of 10 barley genotypes were selected for high grain yield under either high yielding (two groups) or low yielding conditions (two groups). The genotypes had a similar average grain yield across a wide range of yielding conditions, but differed in their linear response over environments (environmental sensitivity). The genotypes selected for high grain yield under low yielding conditions were less sensitive to changing environments than genotypes selected for high grain yield under high yielding conditions. The higher stability of genotypes selected under low yielding conditions was shown by both the linear regression analysis and the comparison of coefficients of variation. The use of a safety-first index showed that the probability of a crop failure of genotypes selected for high grain yield under high yielding conditions was between 1.8 and 2.7 times higher than for genotypes selected for high grain yield under low yielding conditions. The development of new cultivars for areas where a large proportion of the crop is grown by subsistence farmers should therefore be based on selection under low yielding conditions.
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  • 50
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    Applied mathematics and mechanics 12 (1991), S. 1153-1161 
    ISSN: 1573-2754
    Keywords: composites ; circular conical shells ; stability ; potential energy variation principle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, based on the mixed-type theory developed by the same authors[1], a theoretical analysis is presented for the stability of laminated composite circular conical shells under external pressure. The formulas for critical external pressure are obtained by using the potential energy variation principle. Very good agreement is shown between the theoretical prediction of critical external pressure and the experimental data. Finally, the influence of some parameters on critical external pressure is discussed numerically. The mixed-type theory developed by the same authors[1] and the results obtained in this paper are very useful in aerospace engineering design.
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  • 51
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    Pharmaceutical research 8 (1991), S. 1087-1093 
    ISSN: 1573-904X
    Keywords: acyclovir ; prodrugs ; enzymatic hydrolysis ; lipophilicity ; solubility ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Various N-substituted 3- or 4-(aminomethyl)benzoate esters of acyclovir were synthesized and evaluated as water-soluble prodrug forms with the aim of improving the delivery characteristics of acyclovir, in particular its parenteral administration. The esters showed a high solubility in weakly acidic solutions and, as demonstrated with the 3-(N,N-dipropylaminomethyl)benzoate ester, a high stability in such solutions, allowing storage for several years. The esters combine these properties with a high susceptibility to undergo enzymatic hydrolysis in plasma. The half-lives of hydrolysis in 80% human plasma ranged from 0.8 to 57 min, the rate being highly dependent on the position (3 or 4) of the aminomethyl group relative to the ester moiety. All esters were more lipophilic than acyclovir in terms of octanol–pH 7.4 buffer partition coefficients. These properties make N-substituted (aminomethyl)-benzoate esters a promising new prodrug type for acyclovir to enhance its delivery characteristics.
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  • 52
    ISSN: 1573-904X
    Keywords: dexamethasone ; dexamethasone acetate ; complexation ; 2-hydroxypropyl-β-cyclodextrin ; solubility ; stability ; ocular bioavailability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complexation of dexamethasone (DX) and dexamethasone acetate (DXA) with 2-hydroxypropyl-β-cyclodextrin (HPCD) was investigated with an ultimate goal of formulating a topical ophthalmic solution of DXA. Aqueous solubility of DX and DXA was markedly increased due to formation of soluble inclusion complexes with HPCD. Based on characterization of complex formation by phase solubility and UV-spectroscopy methods, a stoichiometry of 1:1 and 1:1, 1:2 was assumed for DX-HPCD and DXA-HPCD complexes, respectively. The stability constants for complex formation estimated by phase solubility and UV-spectroscopy methods, respectively, were as follows: for DX-HPCD complex, Kl :l = 2193 and 2221 M−1; and for DXA-HPCD complex, K 1:1 = 2240 and 2445 M −l and K l:2 = 3 and 17 M −1. K l :l of 2266 M −l and K l :2 of 20 M −l were also estimated for the DXA-HPCD complex by kinetics. The kinetics of DXA degradation in pH 7 phosphate buffer at 25°C followed pseudo first order. The addition of HPCD decreased the rate but the order of reaction remained unchanged. Free DXA degraded at a faster rate than complexed DXA. Ocular bioavailability in conjunctiva, cornea, iris, and aqueous humor postadministration of a 25-µl dose of formulations containing an equivalent of 0.1% (w/v) DX followed a rank-order of DXA-HPCD solution 〉 DXA suspension 〉 DX-HPCD solution 〉 DX suspension.
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  • 53
    ISSN: 1573-904X
    Keywords: liposome ; differential scanning calorimetry (DSC) ; stability ; freezing/thawing ; cryopreservation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal behavior of water in liposome dispersions and in liposome dispersions containing mannitol at subzero temperatures was investigated with differential scanning calorimetry (DSC). The cooling curves from 20 down to - 60°C for a liposome dispersion (bilayer composition PL100H/DCP), monitored at cooling rates of 5 and 10°C/min, showed several heat flows related to water crystallization. All lipid-containing dispersions showed water crystallization at temperatures below −40°C. The magnitude of this heat flow strongly depended on the experimental variables. Cooling rate, particle size, lipid concentration, and location and nature of the cryoprotectant all influenced the water crystallization behavior as shown in the DSC cooling curve. Different fractions of water–presumably related to their location in the dispersion–could be distinguished. It is concluded that DSC provides a valuable tool for the detection of changes in the physical state of water in liposome dispersions during freezing/thawing. The insights gained from these DSC studies may make it possible to select–on the basis of rational considerations rather than by trial and error–optimum conditions for the cryopreservation of liposomes containing water-soluble drugs.
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  • 54
    ISSN: 1573-904X
    Keywords: nitrofurantoin ; anhydrate ; monohydrate ; stability ; hydration ; kinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 55
    ISSN: 1573-904X
    Keywords: imipenem ; metabolite ; assay ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Imipenem (thienamycin formamidine) is an antibiotic active against a broad spectrum of bacteria. Its primary metabolite arises from cleavage of the lactam ring. The metabolite can be formed in-vitro by acid-catalyzed or enzymatic hydrolysis. In animals and man, this metabolite can be generated systemically as well as in the kidneys following the excretion of imipenem into the urine. In man, this dehydropeptidase-catalyzed renal metabolism is minimized by the coadministration of cilastatin, a competitive inhibitor. A specific HPLC assay has been developed to evaluate the disposition of this metabolite in humans having normal or end-stage renal function. The assay employs ion-pair, re versed-phase chromatography, and post-column acid treatment of the analyte for ultraviolet detection.
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  • 56
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    Pharmaceutical research 8 (1991), S. 123-126 
    ISSN: 1573-904X
    Keywords: nonlinear ; Arrhenius ; degradation ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 57
    ISSN: 1573-904X
    Keywords: ibutilide ; shelf life ; stability ; Arrhenius analysis ; nucleophilic substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 58
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    Pharmaceutical research 8 (1991), S. 547-549 
    ISSN: 1573-904X
    Keywords: hydrocortisone 17-butyrate ; steroids ; stability ; topical cream ; high-performance liquid chromatography (HPLC)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 59
    ISSN: 1573-904X
    Keywords: 2-hydroxypropyl-β-cyclodextrin ; ovine growth hormone ; interleukin-2 ; insulin ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A chemically modified, amorphous β-cyclodextrin, namely, 2-hydroxypropyl-β-cyclodextrin (HPCD), was examined as a solubilizing and stabilizing agent for protein drugs. The aqueous solubility of ovine growth hormone at pH 7.4 was increased through the use of HPCD. This effect was manifested by higher UV transparency at 600 nm. Interleukin-2 (IL-2) is rendered insoluble upon lyophilization in the absence of stabilizers. Use of aqueous HPCD provides a clear solution, as indicated by fluorometric light scattering, and inhibits aggregate formation, as shown by ultracentrifugation and Western blot analyses. In addition, there were no major conformational changes of IL-2 in HPCD formulation as indicated by fourth-derivative ultraviolet spectroscopy. Finally, IL-2 retained 100% of its biopotency when prepared in HPCD solutions. Aggregation of insulin was also suppressed by HPCD. These data, as well as the i.v. safety of HPCD and its well-characterized chemical composition, suggest that this starch derivative may be a potentially useful excipient for protein drugs intended for parenteral use.
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  • 60
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    Journal of optimization theory and applications 70 (1991), S. 597-606 
    ISSN: 1573-2878
    Keywords: Interval matrices ; stability ; robustness ; iterative algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper presents new sufficient conditions for the stability of interval matrices. An iterative algorithm, based on the Lyapunov stability approach, is developed. In this way, the stability bounds are increased substantially over the ones recently reported in the literature. Three numerical examples are given to demonstrate the merits of the proposed approach.
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  • 61
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    Nonlinear dynamics 2 (1991), S. 405-417 
    ISSN: 1573-269X
    Keywords: Collocation ; stability ; bifurcation ; modal interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A methodology is first presented for analyzing long time response of periodically exited nonlinear oscillators. Namely, a systematic procedure is employed for determining periodic steady state response, including harmonic and superharmonic components. The stability analysis of the located periodic motions is also performed, utilizing results of Froquet theory. This methodology is then applied to a special class of two degree of freedom nonlinear oscillators, subjected to harmonic excitation. The numberical results presented in the second part of this study illustrate effects caused by the interaction of the modes as well as effects of the nonlinearities on the steady state response of these oscillators. In addition, sequences of bifurcations are analyzed for softening systems, leading to unbounded response of the model examined. Finally, the importance of higher harmonics on the response of systems with strongly nonlinear characteristics is investigated.
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