Adr1 and Cat8 synergistically activate the glucose-regulated alcohol dehydrogenase gene ADH2 of the yeast Saccharomyces cerevisiae

Glucose-repressible alcohol dehydrogenase II, encoded by the ADH2 gene of the yeast Saccharomyces cerevisiae, is transcriptionally controlled by the activator Adr1, binding UAS1 of the control region. However, even in an adr1 null mutant, a substantial level of gene derepression can be detected, arguing for the existence of a further mechanism of activation. Here it is shown that the previously identified UAS2 contains a distantly related variant of the carbon source-responsive element (CSRE) initially found upstream of gluconeogenic genes. In a mutant defective for the CSRE-binding factor Cat8, derepression of an ADH2-lacZ fusion was reduced to about 12 % of the wildtype level. Gene expression in a cat8 adr1 double mutant decreased almost to the basal level of the glucose-repressed promoter. CSREADH2 present in a single copy turned out to be a weak UAS element, while a significant synergism of gene activation was found in the presence of at least two copies. Its importance for regulated gene activation was confirmed by site-directed mutagenesis of the CSRE in the natural ADH2 control region. Direct binding of Cat8 to CSREADH2 could be shown by electrophoretic retardation of the corresponding protein/DNA complex in the presence of a specific antibody. In contrast to what was shown previously for CSRE sequence variants, no significant influence of the isofunctional activator Sip4 on CSREADH2 was detected. In conclusion, these results show a derepression of ADH2 by synergistically acting regulators Adr1 (interacting with UAS1) and Cat8, binding to UAS2 (= CSREADH2).