The regulation of glycolytic genes in response to carbon source in the yeast Saccharomyces cerevisiae has been studied. When the relative levels of each glycolytic mRNA were compared during exponential growth on glucose or lactate, the various glycolytic mRNAs were found to be induced to differing extents by glucose. No significant differences in the stabilities of the PFK2, PGKI, PYKI, or PDCI mRNAs during growth on glucose or lactate were observed. PYK::lacZ and PGK::lacZ fusions were integrated independently into the yeast genome at the ura3 locus. The manner in which these fusions were differentially regulated in response to carbon source was similar to that of their respective wild-type loci. Therefore, the regulation of glycolytic mRNA levels is mediated at the transcriptional level. When the mRNAs are ordered with respect to the glycolytic pathway, two peaks of maximal induction are observed at phosphofructokinase and pyruvate kinase. These enzymes (i) catalyze the two essentially irreversible steps on the pathway, (ii) are the two glycolytic enzymes that are circumvented during gluconeogenesis and hence are specific to glycolysis, and (iii) are encoded by mRNAs that we have shown previously to be coregulated at the translational level in S. cerevisiae (P. A. Moore, A. J. Bettany, and A. J. P. Brown, NATO ASI Ser. Ser. H Cell Biol. 49:421-432, 1990). This differential regulation of glycolytic mRNA levels might therefore have a significant influence upon glycolytic flux in S. cerevisiae.The glycolytic pathway plays a fundamental role in the provision of metabolic energy and intermediates during fermentative growth in the yeast Saccharomyces cerevisiae. Under these conditions, the glycolytic genes are among the most efficiently expressed genes in this organism, the glycolytic enzymes comprising over 30% of soluble cell protein (for reviews, see references 20 and 70). Most yeast glycolytic genes have been isolated and sequenced (2, 4, 11, 21, 23, 25, 27, 29-31, 40, 59, 62, 63, 68, 69). The high-level expression of yeast glycolytic genes is dependent upon complex interactions between a number of cis-acting promoter elements and trans-acting transcription factors which include the RAP1, ABF1, GCR1, and GAL11 proteins (3,8,10,12,13,15,41,48,55,60,61).It is not clear whether the expression of all glycolytic genes is induced when yeast cultures are transferred from nonfermentative to fermentative carbon sources. Maitra and Lobo (37) observed 3-to 100-fold increases in the levels of glycolytic enzymes following the addition of glucose to yeast cultures growing on acetate. This work was performed on a hybrid yeast strain generated by a cross between Saccharomyces fragilis and Saccharomyces dobzhanskii (37). Some more recent studies appear to confirm this observation for S. cerevisiae. For example, analyses of the enolase (EN02), phosphoglygerate kinase (PGKJ), pyruvate kinase (PYKI), pyruvate decarboxylase (PDCI), and alcohol dehydrogenase (ADHI) mRNAs have suggested that their levels are regulated in response to ...

The regulation of glycolytic genes in response to carbon source in the yeast Saccharomyces cerevisiae has been studied. When the relative levels of each glycolytic mRNA were compared during exponential growth on glucose or lactate, the various glycolytic mRNAs were found to be induced to differing extents by glucose. No significant differences in the stabilities of the PFK2, PGK1, PYK1, or PDC1 mRNAs during growth on glucose or lactate were observed. PYK::lacZ and PGK::lacZ fusions were integrated independently into the yeast genome at the ura3 locus. The manner in which these fusions were differentially regulated in response to carbon source was similar to that of their respective wild-type loci. Therefore, the regulation of glycolytic mRNA levels is mediated at the transcriptional level. When the mRNAs are ordered with respect to the glycolytic pathway, two peaks of maximal induction are observed at phosphofructokinase and pyruvate kinase. These enzymes (i) catalyze the two essentially irreversible steps on the pathway, (ii) are the two glycolytic enzymes that are circumvented during gluconeogenesis and hence are specific to glycolysis, and (iii) are encoded by mRNAs that we have shown previously to be coregulated at the translational level in S. cerevisiae (P. A. Moore, A. J. Bettany, and A. J. P. Brown, NATO ASI Ser. Ser. H Cell Biol. 49:421-432, 1990). This differential regulation of glycolytic mRNA levels might therefore have a significant influence upon glycolytic flux in S. cerevisiae.