THE MUTATION DGT1-1 DECREASES GLUCOSE-TRANSPORT AND ALLEVIATES CARBONCATABOLITE REPRESSION IN SACCHAROMYCES-CEREVISIAE

Glucose in ethanol-glycerol mixtures inhibits growth of Saccharomyces cerevisiae mutants lacking phosphoglycerate mutase. A suppressor mutat ion that relieved glucose inhibition was isolated. This mutation, DGT1 -1 (decreasing glucose transport), was dominant and produced pleiotrop ic effects even in an otherwise wild-type background. Growth of the DG T1-1 mutant in glucose was dependent on respiration, and no ethanol wa s detected in the medium within 7 h of glucose addition. When grown on glucose, the mutant had a reduced glucose uptake and both the low- an d high-affinity transport systems were affected. In galactose-grown ce lls, only the high-affinity glucose transport system was detected. Thi s system had similar kinetic characteristics in the wild type and in t he mutant. Catabolite repression of several enzymes was absent in the mutant during growth in glucose but not during growth in galactose. In contrast with the wild type, the mutant grown in glucose had high tra nscription of the glucose transporter gene SNF3 and no transcription o f HXT1 and HTX3. Expression of multicopy plasmids carrying the HXT1, H XT2, or HXT3 gene allowed partial recovery of both fermentative capaci ty and catabolite repression in the mutant. The results suggest that D GT1 codes for a regulator of the expression of glucose transport genes . They also suggest that glucose flux might determine the levels of mo lecules implicated as signals in catabolite repression.