Regulation of the yeast HIS7 gene by the global transcription factor Abf1p.

The HIS7 gene of Saccharomyces cerevisiae encodes a bifunctional glutamine amidotransferase: cyclase that catalyzes the formation of biosynthetic precursors for histidine and adenine. HIS7 is activated by Gcn4p upon amino acid starvation and by the Bas1/2p complex in response to adenine limitation. Mutation analysis of the HIS7 promoter in a deltagcn4 background revealed a polyd(A/T) stretch and a d(CT) repeat as essential elements for Gcn4p-independent basal HIS7 transcription. The protein binding this element was enriched and identified as the multifunctional DNA-binding protein Abf1p. Abf1p binds specifically to the d(CT) repeat sequence, which represents a novel Abf1p-binding motif, and protects 17 nucleotides from digestion by DNase I. In addition, Abf1p binding causes bending of the HIS7 promoter structure.