A single Saccharomyces cerevisiae upstream activation site (UAS1) has two distinct regions essential for its activity.

Several site-directed mutagenesis regimens were used to generate single- and multiple-base substitutions in the upstream activation site UAS1 of the Saccharomyces cerevisiae CYC1 gene. Mutations resulting in large reductions in activity of the site lie in two distinct regions. Six single-base changes in a region A, between -288 and -285, all resulted in a 15-fold reduction in activity. Synthetic sites built up solely of multimers of the -289 to -285 sequence ACCGA behaved as carbon catabolite-sensitive UASs. In addition, substitution mutations in a second region, at nucleotides -266 and -265, virtually eliminated UAS1 activity. These mutations abolished the binding of a heme-dependent protein factor in vitro. Thus, UAS1 contains two essential regions both of which are required for its activity.