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  • 1
    ISSN: 0192-253X
    Keywords: Somatic embryogenesis ; temperature-sensitive mutant ts11 ; chitinase ; carrot (Daucus carota L.) ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: At the nonpermissive temperature, somatic embryos of the temperature-sensitive (ts) carrot (Daucus carota L.) cell variant ts11 only proceed beyond the globular embryo stage in the presence of medium conditioned by wild-type cells. The causative component in the conditioned medium has been identified as an acidic 32 kD endochitinase. An antiserum raised against the 32 kD chitinase detected this protein in culture medium from ts11 embryo cultures grown at the permissive temperature as well as at the nonpermissive temperature. No difference in biochemical characteristics or in effect on ts11 embryo development could be detected between the 32 kD chitinase purified from wild-type cultures and the chitinase from ts11 cultures grown at the permissive or at the nonpermissive temperature. Compared to the amount present in a ts11 embryo culture at the permissive temperature, a reduction in the amount of 32 kD chitinase was observed during the temperature-sensitive period at the nonpermissive temperature. These results imply that the arrested embryo phenotype of ts11 is not the result of a structural difference in its 32 kD chitinase, but is the result of a transient decrease in the amount of 32 kD chitinase present. Morphological observations indicate that the ts11 phenotype is pleiotropic and also affects the cell wall of nonembryogenic cells. © 1995 Wiley-Liss, Inc.
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  • 2
    ISSN: 0749-503X
    Keywords: Orthgonal-field-alternation gel electrophoresis ; karyotyping ; ascomycetous yeasts ; basidiomycetous yeasts ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Chromosomal DNAs from various yeast species were separated by orthogonal-field-alternation gel electrophoresis (OFAGE). To this end we developed a spheroplasting and lysis method to obtain intact DNA from both ascomycetous and basidiomycetous yeasts. The OFAGE banding patterns of 22 ascomycetous and four basidiomycetous yeast strains were compared. The strains represented species from the genera: Brettanomyces, Candida, Croococcus, Filobasidiella, Geotrichum, Hansenula, Kluyveromyces, Pachysolen, Pichia, Rhodosporidium, Rhodotorula, Saccharomyces, Saccharomycodes, Saccharomycopis, Schizosaccharomyces and Zygosaccharomyces. Variations occurred in the number of bands and their positions in the gel, not only among strains of different genera but also among species from the same genus and even between varieties of the same species. The ascomycetous yeasts, with the exeption of Saccharomyces cerevisiae, only showed one to five bands of DNA larger than 1000 kilobase pairs (kb) in general none smaller. The paterns of the four basidiomycetous yeasts revealed also a few large DNA bands but in addition one to six bands ranging in size from 500 to 1000 kb, with the exception of a single smaller chromosome in Rhodotorula mucilaginosa. From the OFAGE banding patterns of strains studied here it appears that in Saach. cerevisiae the partitioning of DNA over chromosomes in unique. But rather than the large number of chromosomes, the presence of four chromosomes with less than 500 kb of DNA is characteristic for Sacch. cerevisiae.
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  • 3
    ISSN: 0749-503X
    Keywords: hexokinase PII ; glycolysis ; Tps1 ; fermentation ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In the yeast Saccharomyces cerevisiae a novel control exerted by TPS1 (=GGS1=FDP1=BYP1=CIF1=GLC6=TSS1)-encoded trehalose-6-phosphate synthase, is essential for restriction of glucose influx into glycolysis apparently by inhibiting hexokinase activity in vivo. We show that up to 50-fold overexpression of hexokinase does not noticeably affect growth on glucose or fructose in wild-type cells. However, it causes higher levels of glucose-6-phosphate, fructose-6-phosphate and also faster accumulation of fructose-1,6-bisphosphate during the initiation of fermentation. The levels of ATP and Pi correlated inversely with the higher sugar phosphate levels. In the first minutes after glucose addition, the metabolite pattern observed was intermediate between those of the tps1Δ mutant and the wild-type strain. Apparently, during the start-up of fermentation hexokinase is more rate-limiting in the first section of glycolysis than phosphofructokinase. We have developed a method to measure the free intracellular glucose level which is based on the simultaneous addition of d-glucose and an equal concentration of radiolabelled l-glucose. Since the latter is not transported, the free intracellular glucose level can be calculated as the difference between the total d-glucose measured (intracellular+periplasmic/extracellular) and the total l-glucose measured (periplasmic/extracellular). The intracellular glucose level rose in 5 min after addition of 100 mm-glucose to 0·5-2 mm in the wild-type strain, ±10 mm in a hxk1Δ hxk2Δ glk1Δ and 2-3 mm in a tps1Δ strain. In the strains overexpressing hexokinase PII the level of free intracellular glucose was not reduced. Overexpression of hexokinase PII never produced a strong effect on the rate of ethanol production and glucose consumption. Our results show that overexpression of hexokinase does not cause the same phenotype as deletion of Tps1. However, it mimics it transiently during the initiation of fermentation. Afterwards, the Tps1-dependent control system is apparently able to restrict properly up to 50-fold higher hexokinase activity. © 1998 John Wiley & Sons, Ltd.
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  • 4
    ISSN: 0749-503X
    Keywords: Cell wall porosity ; permeability ; polycation assay ; cell wall structure ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have developed a new assay to determine relative cell wall porosity in yeasts, which is based on polycation-induced leakage of UV-absorbing compounds. Polycations with a small hydrodynamic radius as measured by gel filtration (poly-L-lysine) caused cell leakage independent of cell wall porosity whereas polycations with a large hydrodynamic radius (DEAE-dextrans) caused only limited cell leakage due to limited passage through the cell wall. This allowed the ratio between DEAE-dextran- and poly-L-lysine-induced cell leakage to be used as a measure of cell wall porosity in Saccharomyces cerevisiae, Kluyveromyces lactis and Schizosaccharomyces pombe. Using this assay, we found that the composition of the growth medium affected cell wall porosity in S. cerevisiae. In addition, we could show that cell wall porosity is limited by the number of disulphide bridges in the wall and is dependent on cell turgor. It is argued that earlier methods to estimate cell wall porosity in S. cerevisiae resulted in large underestimations.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 8 (1992), S. 39-45 
    ISSN: 0749-503X
    Keywords: Flow cytometry ; autolytic mutants ; protoplasts ; yeast ; viability assay ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Simple methods, based on the technique of flow cytometry, have been developed for the phenotypic characterization of yeast autolytic mutants and for the analysis of the formation and regeneration of the yeast protoplasts. The expression of lytic mutations determined uptake of the fluorescent dye propidium iodide, which could be carefully monitored by flow cytometry. Mixed populations of lysed and viable cells were precisely quantified and sorted, and the technique was also applied to demonstrate protection from lysis of mutant cells with cell wall defects, in the presence of osmotic stabilizers. Protoplast formation and regeneration was monitored by analysing relative cell size; this was facilitated by the preparation of homogeneous protoplast preparations. The technique of flow cytometry proved superior to other conventional methods for these types of study.
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  • 6
    ISSN: 0749-503X
    Keywords: Amine oxidase ; peroxisomes ; Hansenula polymorpha ; Saccharomyces cerevisiae ; targeting signal ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Amine oxidase from the yeast Hansenula polymorpha is a peroxisomal protein. The signal for routing of the protein into peroxisomes has not been identified yet. Expression of a mutant amine oxidase in H. Polymorpha has revealed that the C-terminal sequence, which possesses an internal SRL tripeptide, is not involved in targeting (Faber et al., unpublished). We have explored heterologous expression of the amine oxidase gene (AMO) in Saccharomyces cerevisiae to investigate the conservation of peroxisomal targeting pathways between yeasts. Surprisingly, wide-type amine oxidase is not recognized as a peroxisomal protein by S. cerevisiae. The enzyme, which was fully active and acumulated to levels similar to those found in H. polymorpha, stayed entirely in the cytosol. However, fusing a SKL or a SRL sequence to the C-terminus forced the protein at least partially into peroxisomes of the heterologous host. These data suggest that the functional targeting sequence of amine oxidase may differ from the C-terminal peroxisomal targeting signal S/C/A-K/R/H-L (Gould et al., 1989). Contrary to the established tripeptide motif, the amine oxidase targeting signal appears not to be conserved between the different yeast species.
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  • 7
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; protein kinase ; mRNA leader ; RAS ; cell cycle ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The SCH9 yeast gene, that was previously identified as a suppressor of cdc25 and ras1- ras2-ts temperature-sensitive mutants, encodes a putative protein kinase that positively regulates the progression of yeast cells through the G1 phase of the cell cycle. We have determined the structure of the SCH9 transcription unit, using primer extension and S1 mapping techniques. The corresponding mRNA included an unusually long 5′ region of more than 600 nucleotides preceding the major open reading frame (ORF). While the latter corresponded to a protein of 824 amino acids, an upstream open reading frame (uORF) within the 5′ leader could potentially encode a 54 amino acid peptide. To investigate the role of the AUGs within the uORF, we engineered chimaeric plasmid vectors in which SCH9 sequences including the promoter, the mRNA leader and the first 514 nucleotides of the major ORF were fused in-frame with β-galactosidase-coding sequences. Upon introduction into yeast cells, the fusion protein was efficiently expressed. However, mutational disruption of the uORF using oligonucleotide-directed mutagenesis did not affect the level of expression of the fusion protein. This indicates that regulatory mechanisms in Saccharomyces cerevisiae prevent upstream AUGs within the SCH9 mRNA leader sequence from influencing translation from downstream initiation codons.
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  • 8
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; chromosome I ; calnexin homologue ; CNE1 ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
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  • 9
    ISSN: 0749-503X
    Keywords: chemostat ; mixed substrates ; gluconeogenesis ; glyoxylate cycle ; Saccharomyces cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Growth efficiency and regulation of key enzyme activities were studied in carbon- and energy-limited chemostat cultures of Saccharomyces cerevisiae grown on mixtures of glucose and ethanol at a fixed dilution rate. Biomass yields on substrate carbon and oxygen could be adequately described as the net result of growth on the single substrates. Activities of isocitrate lyase and malate synthase were not detected in cell-free extracts of glucose-limited cultures. However, both enzymes were present when the ethanol fraction in the reservoir medium exceeded the theoretical minimum above which the glyoxylate cycle is required for anabolic reactions. Fructose-1,6-bisphosphatase activity was only detectable at high ethanol fractions in the feed, when activity of this enzyme was required for synthesis of hexose phosphates. Phospho-enol-pyruvate-carboxykinase activity was not detectable in extracts from glucose-grown cultures and increased with the ethanol fraction in the feed. It is concluded that, during carbon-limited growth of S. cerevisiae on mixtures of glucose and ethanol, biosynthetic intermediates with three or more carbon atoms are preferentially synthesized from glucose. Synthesis of the key enzymes of gluconeogenesis and the glyoxylate cycle is adapted to the cells′ requirement for these intermediates. The gluconeogenic enzymes and their physiological antagonists (pyruvate kinase, pyruvate carboxylase and phosphofructokinase) were expressed simultaneously at high ethanol fractions in the feed. If futile cycling is prevented under these conditions, this is not primarily achieved by tight control of enzyme synthesis.
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  • 10
    ISSN: 0749-503X
    Keywords: arginine regulation ; ARG1 ; ARG8 ; CPA1 ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Repression or induction of the genes involved in arginine biosynthesis or catabolism, respectively, both require participation of the ArgRp/Mcm1p regulatory complex. Our previous work showed that those opposite effects were mediated by a similar arginine-responsive element of 23 nucleotides (that we now call ARC, for ARginine Control) situated close to the start of transcription in the repressed promoters and far upstream of the TATA-element in the induced promoters.To define more precisely the sequence and position requirements of the ARC element, we have now characterized by mutagenesis the promoter elements of the arginine-repressible ARG1 and ARG8 genes. We also identify a functional ARC in the CPA1 promoter, thereby confirming, in agreement with our previous mRNA pulse-labelling data, the participation of a transcriptional component in the arginine regulation of that gene otherwise submitted to a translational regulation.From the 12 ARC elements now characterized, we have derived a consensus sequence and show that such a synthetic element is able to mediate ArgRp/Mcm1p-dependent arginine regulation.An important new finding illustrated by ARG1 and CPA1, is that contrary to what all the previous data suggested, repression can be mediated by ARC elements located far upstream of the TATA-box. The new data suggest that the arginine repressor might inhibit transcription in an active process.
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