Evidence for the involvement of the Glc7-Reg1 phosphatase and the Snf1-Snf4 kinase in the regulation of INO1 transcription in Saccharomyces cerevisiae

Binding of the TATA-binding protein (TBP) to the promoter is a pivotal step in RNA polymerase II transcription. To identify factors that regulate TBP, we selected for suppressors of a TBP mutant that exhibits promoter-specifi c defects in activated transcription in vivo and severely reduced affinity for TATA boxes in vitro. Dominant mutations in SNF4 and recessive mutations in REG1, OPI1, and RTF2 were isolated that specifically suppress the inosi tol auxotrophy of the TBP mutant strains. OPI1 encodes a repressor of INO1 transcription. REG1 and SNF4 encode regulators of the Glc7 phosphatase and Snf1 kinase, respectively, and have well-studied roles in glucose repressio n. In two-hybrid assays, one SNF4 mutation enhances the interaction between Snf4 and Snf1. Suppression of the TBP mutant by our reg1 and SNF4 mutation s appears unrelated to glucose repression, since these mutations do not all eviate repression of SUC2, and glucose levels have little effect on INO1 tr anscription. Moreover, mutations in TUP1, SSN6,and GLC7 but not HXK2 and MI G1, can cause suppression. Our data suggest that association of TBP with th e TATA box may be regulated, directly or indirectly, by a substrate of Snf1 . Analysis of INO1 transcription in various mutant strains suggests that th is substrate is distinct from Opil.