A deletion of the PDC1 gene for pyruvate decarboxylase of yeast causes a different phenotype than previously isolated point mutations

Abstract

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 necessary for glucose fermentation in yeast.

Characterization of PDC6, a third structural gene for pyruvate decarboxylase in Saccharomyces cerevisiae

“…Thus, the presence ofjust PDCJ is sufficient for the cells to achieve full PDC activity, and as observed before (12,19), deletion of PDCJ can be partially compensated for by PDC5 in glucose but not in ethanol medium. The Apdc6 deletion did not change the PDC activity in any of the strains after growth with glucose.…”

“…Southern blots with genomic yeast DNA were hybridized under reduced stringency with the EcoRIBglII fragment of the PDCJ coding region (19) as probe. Reduced stringency was achieved by slowly decreasing the temperature during hybridization from 68 to 45°C (8 h at 68°C, 2 h to decrease to 45°C, and 4 h at 45°C), omitting the final high-stringency' wash and otherwise following the instructions in the Boehringer (Mannheim, Germany) dioxigenin labeling and detection kit.…”

“…1). This sequence was cloned on a BamHI fragment from strain YSH 149 (Table 1) after preparation of partial genomic libraries and colony hybridization as described previously (19).…”

“…The effect was shown to be due to enhanced expression of PDC5, a second closely related and normally only weakly expressed structural gene for PDC (12,19,23). Thus, in addition to being induced by glucose (12,20), the expression of the PDC genes seems to be under autoregulation at the transcriptional level (11,12).…”

“…tants turned out to grow well on glucose and they had only slightly reduced PDC activity (19,23). The effect was shown to be due to enhanced expression of PDC5, a second closely related and normally only weakly expressed structural gene for PDC (12,19,23).…”