A MUTATION AFFECTING CARBON CATABOLITE REPRESSION SUPPRESSES GROWTH DEFECTS IN PYRUVATE-CARBOXYLASE MUTANTS FROM SACCHAROMYCES-CEREVISIAE

Yeasts with disruptions in the genes PYC1 and PYC2 encoding the isoenz ymes of pyruvate carboxylase cannot grow in a glucose-ammonium medium (Stucka et al. (1991) Mol. Gen. Genet. 229, 307-315). We have isolated a dominant mutation, BPC1-1, that allows growth in this medium of yea sts with interrupted PYC1 and PYC2 genes, The BPC1-1 mutation abolishe s catabolite repression of a series of genes and allo,vs expression of the enzymes of the glyoxylate cycle during growth in glucose, A funct ional glyoxylate cyle is necessary for suppression as a disruption of gene ICL1 encoding isocitrate lyase abolished the phenotypic effect of BPC1-1 on growth in glucose-ammonium. Concurrent expression from cons titutive promoters of genes ICL1 and MLS1 (encoding malate synthase) a lso suppressed the growth phenotype of pyc1 pyc2 mutants. The mutation BPC1-1 is either allelic or closely linked to the mutation DGT1-1.