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  • 1
    Electronic Resource
    Electronic Resource
    Physiological characterisation of a pyruvate-carboxylase-negative Saccharomyces cerevisiae mutant in batch and chemostat cultures (1998)
    Springer
    Antonie van Leeuwenhoek 74 (1998), S. 253-263 
    Details
    ISSN: 1572-9699
    Keywords: Saccharomyces cerevisiae ; pyruvate carboxylase ; anaplerotic reactions ; sugar metabolism ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A prototrophic pyruvate-carboxylase-negative (Pyc-) mutant was constructed by deleting the PYC1 and PYC2 genes in a CEN.PK strain of Saccharomyces cerevisiae. Its maximum specific growth rate on ethanol was identical to that of the isogenic wild type but it was unable to grow in batch cultures in glucose-ammonia media. Consistent with earlier reports, growth on glucose could be restored by supplying aspartate as a sole nitrogen source. Ethanol could not replace aspartate as a source of oxaloacetate in batch cultures. To investigate whether alleviation of glucose repression allowed expression of alternative pathways for oxaloacetate synthesis, the Pyc- strain and an isogenic wild-type strain were grown in aerobic carbon-limited chemostat cultures at a dilution rate of 0.10 h-1 on mixtures of glucose and ethanol. In such mixed-substrate chemostat cultures of the Pyc- strain, steady-state growth could only be obtained when ethanol contributed 30% or more of the substrate carbon in the feed. Attempts to further decrease the ethanol content of the feed invariably resulted in washout. In Pyc- as well as in wild-type cultures, levels of isocitrate lyase, malate synthase and phospho-enol-pyruvate carboxykinase in cell extracts decreased with a decreasing ethanol content in the feed. Nevertheless, at the lowest ethanol fraction that supported growth of the Pyc- mutant, activities of the glyoxylate cycle enzymes in cell extracts were still sufficient to meet the requirement for C4-compounds in biomass synthesis. This suggests that factors other than glucose repression of alternative routes for oxaloacetate synthesis prevent growth of Pyc-mutants on glucose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001772613615
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation of carbon metabolism in chemostat cultures of Saccharomyces cerevisiae grown on mixtures of glucose and ethanol (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 11 (1995), S. 407-418 
    Details
    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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320110503
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  • 3
    Electronic Resource
    Electronic Resource
    Transient mRNA responses in chemostat cultures as a method of defining putative regulatory elements: Application to genes involved in Saccharomyces cerevisiae acetyl-coenzyme A metabolism (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 1089-1104 
    Details
    ISSN: 0749-503X
    Keywords: chemostat cultivation ; Saccharomyces cerevisiae ; carbon source ; transcriptional regulation ; UAS ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: To identify common regulatory sequences in the promoters of genes, transcription of 31 genes of Saccharomyces cerevisiae was analysed during the transient response to a glucose pulse in a chemostat culture. mRNA levels were monitored during the subsequent excess glucose, ethanol and acetate phases, while other conditions were kept constant. This setup allowed a direct comparison between regulation by glucose, ethanol and acetate.Genes with identical regulation patterns were grouped to identify regulatory elements in the promoters. In respect to regulation on glucose four classes were identified: no transcription under any of the conditions tested, no difference in regulation on glucose, induced on glucose and repressed on glucose. In addition, genes were found that were repressed or induced on ethanol or acetate. Sequence alignment of genes with similar regulation patterns revealed five new, putative regulatory promoter elements. (i) The glucose-inducible fermentation genes PDC1 and ADH1 share the sequence ATACCTTCSTT. (ii) Acetate-repression might be mediated by the decamer CCCGAG RGGA, present in the promoters of ACS2 and ACR1. (iii) A specific element (CCWTTSRNCCG) for the glyoxylate cycle was present in seven genes studied: CIT2, ICL1, MLS1, MDH2, CAT2, ACR1 and ACH1. These genes were derepressed on ethanol or acetate. (iv) The sequence ACGTSCRGAATGA was found in the promoters of the partially ethanol-repressed genes ACS1 and YAT1. (v) Ethanol induction, as seen for ACS2, ADH3 and MDH1, might be mediated via the sequence CGGSGCCGRAG. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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