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

Abstract

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 bc1 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 sci1-1 is attributable to a decrease in glycolytic flux.