ABSTRACT

Recessive mutations in two negative control elements, CRE1 and CRE2, have been obtained that allow the glucose-repressible alcohol dehydrogenase (ADHII) of yeast to escape repression by glucose. Both the cre1 and cre2 alleles affected ADHII synthesis irrespective of the allele of the positive effector, ADR1. However, for complete derepression of ADHII synthesis, a wild-type ADR1 gene was required. Neither the cre1 nor cre2 alleles affected the expression of several other glucose-repressible enzymes. A third locus, CCR4, was identified by recessive mutations that suppressed the cre1 and cre2 phenotypes. The ccr4 allele blocked the derepression of ADHII and several other glucose-repressible enzymes, indicating that the CCR4 gene is a positive control element. The ccr4 allele had no effect on the repression of ADHII when it was combined with the ADR1-5^c allele, whereas the phenotypically similar ccr1 allele, which partially suppresses ADR1-5^c, did not suppress the cre1 or cre2 phenotype. Complementation studies also indicated that ccr1 and snf1 are allelic. A model of ADHII regulation is proposed in which both ADR1 and CCR4 are required for ADHII expression. CRE1 and CRE2 negatively control CCR4, whereas CCR1 is required for ADR1 function.