Mode of action of the qcr9 and cat3 mutations in restoring the ability of Saccharomyces cerevisiae tps1 mutants to grow on glucose

Mutations in the TPS1 gene, which encodes trehalose-6-P synthase, cause a glucose-negative phenotype in Saccharomyces cerevisiae. Antimycin A or disruption of the QCR9 gene, which encodes one subunit of the cytochrome bc(1) complex, restore the ability to grow in glucose-containing media. Under these conditions the cell excreted a large amount of glycerol, corresponding to about 20% of the glucose taken up. Suppression appears to be achieved by diversion of accumulated glycolytic intermediates to the production of glycerol, thereby providing NAD(+) and phosphate for the glyceraldehyde-3-P dehydrogenase reaction. Analysis of the mutation sci1-1, which also suppresses the glucose-negative phenotype of tps1 mutants, showed that glucose transport was decreased in sci1-1 mutants. The gene SCI1 was cloned and its nucleotide sequence revealed it to be identical to CAT3/SNF4. The suppression mediated by scil-1 is attributable to a decrease in glycolytic flux.