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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A major part of the transcriptional response of yeast cells to osmotic shock is controlled by the HOG pathway and several downstream transcription factors. Sko1p is a repressor that mediates HOG pathway-dependent regulation by binding to CRE sites in target promoters. Here, we report five target genes of Hog1p–Sko1p: GRE2, AHP1, SFA1, GLR1 and YML131w. The two CREs in the GRE2 promoter function as activating sequences and, hence, bind (an) activator protein(s). However, the two other yeast CRE-binding proteins, Aca1p and Aca2p, are not involved in regulation of the GRE2 promoter under osmotic stress. In the absence of the co-repressor complex Tup1p–Ssn6p/Cyc8p, which is recruited by Sko1p, stimulation by osmotic stress is still observed. These data indicate that Sko1p is not only required for repression, but also involved in induction upon osmotic shock. All five Sko1p targets encode oxidoreductases with demonstrated or predicted roles in repair of oxidative damage. Altered basal expression levels of these genes in hog1Δ and sko1Δ mutants may explain the oxidative stress phenotypes of these mutants. All five Sko1p target genes are induced by oxidative stress, and induction involves Yap1p. Although Sko1p and Yap1p appear to mediate osmotic and oxidative stress responses independently, Sko1p may affect Yap1p promoter access or activity. The five Sko1p target genes described here are suitable models for studying the interplay between osmotic and oxidative responses at the molecular and physiological levels.
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The accumulation of compatible solutes, such as glycerol, in the yeast Saccharomyces cerevisiae, is a ubiquitous mechanism in cellular osmoregulation. Here, we demonstrate that yeast cells control glycerol accumulation in part via a regulated, Fps1p-mediated export of glycerol. Fps1p is a member of the MIP family of channel proteins most closely related to the bacterial glycerol facilitators. The protein is localized in the plasma membrane. The physiological role of Fps1p appears to be glycerol export rather than uptake. Fps1Δ mutants are sensitive to hypo-osmotic shock, demonstrating that osmolyte export is required for recovery from a sudden drop in external osmolarity. In wild-type cells, the glycerol transport rate is decreased by hyperosmotic shock and increased by hypo-osmotic shock on a subminute time scale. This regulation seems to be independent of the known yeast osmosensing HOG and PKC signalling pathways. Mutants lacking the unique hydrophilic N-terminal domain of Fps1p, or certain parts thereof, fail to reduce the glycerol transport rate after a hyperosmotic shock. Yeast cells carrying these constructs constitutively release glycerol and show a dominant hyperosmosensitivity, but compensate for glycerol loss after prolonged incubation by glycerol overproduction. Fps1p may be an example of a more widespread class of regulators of osmoadaptation, which control the cellular content and release of compatible solutes.
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Synthesis of trehalose in the yeast Saccharomyces cerevisiae is catalysed by the trehalose-6-phosphate (Tre6P) synthase/phosphatase complex, which is composed of at least three different subunits encoded by the genes TPS1, TPS2, and TSL1. Previous studies indicated that Tps1 and Tps2 carry the catalytic activities of trehalose synthesis, namely Tre6P synthase (Tps1) and Tre6P phosphatase (Tps2), while Tsl1 was suggested to have regulatory functions. In this study two different approaches have been used to clarify the molecular composition of the trehalose synthase complex as well as the functional role of its potential subunits. Two-hybrid analyses of the in vivo interactions of Tps1, Tps2, Tsl1, and Tps3, a protein with high homology to Tsl1, revealed that both Tsl1 and Tps3 can interact with Tps1 and Tps2; the latter two proteins also interact with each other. In addition, trehalose metabolism upon heat shock was analysed in a set of 16 isogenic yeast strains carrying deletions of TPS1, TPS2, TSL1, and TPS3 in all possible combinations. These results not only confirm the previously suggested roles for Tps1 and Tps2, but also provide, for the first time, evidence that Tsl1 and Tps3 may share a common function with respect to regulation and/or structural stabilization of the Tre6P synthase/phosphatase complex in exponentially growing, heat-shocked cells.
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cells of the yeast Saccharomyces cerevisiae display a wide range of glucose-induced regulatory phenomena, including glucose-induced activation of the RAS-adenylate cyclase pathway and phosphatidylinositol turnover, rapid post-translational effects on the activity of different enzymes as well as long-term effects at the transcriptional level. A gene called GGS1 (for General Glucose Sensor) that is apparently required for the glucose-induced regulatory effects and several ggs1 alleles (fdp1, byp1 and cif1) has been cloned and characterized. A GGS1 homologue is present in Methanobacterium thermoautotrophicum. Yeast ggs1 mutants are unable to grow on glucose or related readily fermentable sugars, apparently owing to unrestricted influx of sugar into glycolysis, resulting in its rapid deregulation. Levels of intracellular free glucose and metabolites measured over a period of a few minutes after addition of glucose to cells of a ggsi1Δ strain are consistent with our previous suggestion of a functional interaction between a sugar transporter, a sugar kinase and the GGS1 gene product. Such a glucose-sensing system might both restrict the influx of glucose and activate several signal transduction pathways, leading to the wide range of glucose-induced regulatory phenomena. Deregulation of these pathways in ggs1 mutants might explain phenotypic defects observed in the absence of glucose, e.g. the inability of ggs1 diploids to sporulate.
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  • 7
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In the yeast Saccharomyces cerevisíae, trehalose-6-phosphate (tre-6-P) synthase encoded by GGS1/TPS1, is not only involved in the production of trehalose but also in restriction of sugar influx into glycolysis in an unknown fashion; it is therefore essential for growth on glucose or fructose. In this work, we have deleted the TPS2 gene encoding tre-6-P phosphatase in a strain which displays very low levels of Ggs1/Tps1, as a result of the presence of the byp1-3 allele of GGS1/TPS1. The byp1-3 tps2Δ double mutant showed elevated tre-6-P levels along with improved growth and ethanol production, although the estimated concentrations of glycolytic metabolites indicated excessive sugar influx. In the wild-type strain, the addition of glucose caused a rapid transient increase of tre-6-P. In tps2Δ mutant cells, which showed a high tre-6-P level before glucose addition, sugar influx into glycolysis appeared to be diminished. Furthermore, we have confirmed that tre-6-P inhibits the hexokinases in vitro. These data are consistent with restriction of sugar influx into glycolysis through inhibition of the hexokinases by tre-6-P during the switch to fermentative metabolism. During logarithmic growth on glucose the tre-6-P level in wild-type cells was lower than that of the byp1-3 tps2Δ. mutant. However, the latter strain arrested growth and ethanol production on glucose after about four generations. Hence, other mechanisms, which also depend on Ggs1/Tps1, appear to control sugar influx during growth on glucose. In addition, we provide evidence that the requirement for Ggs1/Tps1 for sporulation may be unrelated to its involvement in trehalose metabolism or in the system controlling glycolysis.
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  • 8
    ISSN: 1432-0983
    Keywords: Alcoholic fermentation ; Deletion mutant ; Pyruvate decarboxylase ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We deleted most of the pyruvate decarboxylase structural gene PDC1 from the genome of Saccharomyces cerevisiae. Surprisingly, mutants carrying this deletion allele showed a completely different phenotype than previously described point mutations. They were able to ferment glucose and their specific pyruvate decarboxylase activity was only reduced to 45% of the wild type level. Northern blot analysis revealed that a sequence in the yeast genome homologous to PDC1 and formerly designated as a possible pseudogene is expressed and may code for a different but closely related pyruvate decarboxylase. The products of the two PDC genes seem to form hybrid oligomers, however both homooligomers have enzyme activity. Thus, the product of the PDC1 gene is not absolutely neccessary for glucose fermentation in yeast.
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  • 9
    ISSN: 1432-0983
    Keywords: Yeast ; Pyruvate decarboxylase ; Gene expression ; Codon usage ; Gene fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three structural genes encode the pyruvate decarboxylase isoenzymes in the yeast Saccharomyces cerevisiae. PDC1 and PDC5 are active during glucose fermentation where PDC1 is expressed about six times more strongly than PDC5. Expression of PDC6 is weak and seems to be induced in ethanol medium. Consequently, pdc1Δ pdc5Δ double mutants do not ferment glucose and do not grow on glucose medium. Spontaneous mutants, derived from such a pdc1 pdc5 strain, were isolated which could again ferment glucose. They showed pyruvate decarboxylase activity due to a duplication of PDC6. The second copy of PDC6 was expressed under the control of the PDC1 promoter, which was still present in the pdc1 strain. However, the resulting PDC1-PDC6 fusion gene could only partially substitute for PDC1: to achieve normal growth and high pyruvate decarboxylase activity strains carrying PDC1-PDC6 required a functional PDC5 gene which is dispensable in a PDC1 wild-type background. Thus, expression of PDC5 depends on the state of the PDC1 locus: low in the PDC1 wild-type background and high in PDC1-PDC6 fusion strains and, as shown previously, in pdc1 mutants. The activation of PDC5 expression in PDC1-PDC6 strains may be due to particular properties of the PDC1-PDC6 fusion protein or simply to the weaker expression of PDC1-PDC6 in comparison to the wild-type PDC1 gene.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 11 (1986), S. 217-225 
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Gene cloning ; Invertase genes ; Multicopy vector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Six unlinked loci for invertase structural genes are known in the yeast Saccharomyces cerevisiae: SUC1-SUC5 and SUC7. These genes are similar in structure and expression but not identical. Different yeast strains possess none, one or several of these genes. We have isolated the genes SUC1-SUC5, subcloned them into the multicopy vector YEp24 and compared the expression of the five SUC genes in one recipient strain. SUC2 was isolated by transformation of a suc0 strain with a gene pool and complementation to sucrose fermentation. SUC4 was cloned from a minipool of chromosomal fragments which were shown to contain SUC4 by Southern hybridization. SUC1, SUC3 and SUC5 were isolated using the method of plasmid eviction. A plasmid containing regions flanking SUC4 was integrated next to these SUC genes. The plasmid together with the SUC genes were then cut out of the chromosome using an appropriate restriction endonuclease. The length of chromosomal DNA fragments containing the different SUC genes were 4.8 kb for SUC1, 5.2 kb for SUC2, 4.8 kb for SUC3, 12.8 kb for SUC4 and 17.2 kb for SUC5. Fragments containing the complete SUC genes and the sequences controlling their expression were subcloned into YEp24 and transformed into a strain without any active invertase gene. Invertase activity of transformants was measured after growth repressing (8% glucose) and derepressing (2% raffinose) conditions. As expected from results with strains carrying the individual SUC genes in a chromosomal location, the SUC genes were expressed to a different extent.
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