A YEAST TATA-BINDING PROTEIN MUTANT THAT SELECTIVELY ENHANCES GENE-EXPRESSION FROM WEAK RNA-POLYMERASE-II PROMOTERS

We describe a unique gain-of-function mutant of the TATA binding prote in (TBP) subunit of Saccharomyces cerevisiae TFIID that, at least in p art, renders transcriptional transactivators dispensable for efficient mRNA expression. The yTBPN69S mutant enhances transcription from weak er yeast promoter elements by up to 50-fold yet does not significantly increase gene expression directed by highly active promoters, Therefo re, this TBP mutant and transcriptional transactivators appear to affe ct a common rate-limiting step in transcription initiation, Consistent with the hypothesis that this step is TFIID recruitment, tethering of TBP to a target promoter via a heterologous DNA binding domain, which is known to bypass the need for transcriptional transactivators, also nullifies the enhancing effect exerted by the N69S mutation. These da ta provide genetic support for the hypothesis that TFIID recruitment r epresents a rate limiting step in the initiation of mRNA transcription that is specifically enhanced by transcriptional transactivators.