A genome-wide housekeeping role for TFIID and a highly regulated stress-related role for SAGA in Saccharomyces cerevisiae.

TFIID and SAGA share a common set of TAFs, regulate chromatin, and deliver TBP to promoters. Here we examine their relationship within the context of the Saccharomyces cerevisiae genome-wide regulatory network. We find that while TFIID and SAGA make overlapping contributions to the expression of all genes, TFIID function predominates at approximately 90% and SAGA at approximately 10% of the measurable genome. Strikingly, SAGA-dominated genes are largely stress induced and TAF independent, and are downregulated by the coordinate action of a variety of chromatin, TBP, and RNA polymerase II regulators. In contrast, the TFIID-dominated class is less regulated, but is highly dependent upon TAFs, including those shared between TFIID and SAGA. These two distinct modes of transcription regulation might reflect the need to balance inducible stress responses with the steady output of housekeeping genes.