Post-translational regulation of Adr1 activity is mediated by its DNA binding domain

1ADRI encodes a transcriptional activator that regulates genes involved in carbon source utilization in Saccharomyces cerevisiae. ADR1 is itself repre ssed by glucose, but the significance of this repression for regulating tar get genes is not known. To test if the reduction in Adr1 levels contributes to glucose repression of ADH2 expression, we generated yeast strains in wh ich the level of Adr1 produced during growth in glucose-containing medium i s similar to that present in wildtype cells grown in the absence of glucose . In these Adr1-overproducing strains, ADH2 expression remained tightly rep ressed, and UAS1, the element in the ADH2 promoter that binds Adr1, was suf ficient to maintain glucose repression. Post-translational modification of Adr1 activity is implicated in repression, since ADH2 derepression occurred in the absence of de novo protein synthesis. The N-terminal 172 amino acid s of Adr1, containing the DNA binding and nuclear localization domains, fus ed to the Herpesvirus VP16-encoded transcription activation domain, conferr ed regulated expression at UAS1, Nuclear localization of an Adr1-GFP fusion protein was not glucose-regulated, suggesting that the DNA binding domain of Adr1 is sufficient to confer regulated expression on target genes, A Ga1 4-Adr1 fusion protein was unable to confer glucose repression at GALA-depen dent promoters, suggesting that regulation mediated by ADR1 is specific to UAS1.