EVIDENCE THAT SPT3 FUNCTIONALLY INTERACTS WITH MOT1, TFIIA, AND TATA-BINDING PROTEIN TO CONFER PROMOTER-SPECIFIC TRANSCRIPTIONAL CONTROL INSACCHAROMYCES-CEREVISIAE

Spt3 of Saccharomyces cerevisiae is a factor required for normal trans cription from particular RNA polymerase II-dependent promoters, Previo us genetic and biochemical analyses have shown that Spt3 interacts wit h the yeast TATA-binding protein (TBP), To identify other factors that might interact with Spt3, we have screened for mutations that, in com bination with an spt3 null mutation, lead to inviability. In this way, we have identified a mutation in MOT1, which encodes an ATP-dependent inhibitor of TBP binding to TATA boxes. Previous analyses suggested t hat Mot1 causes repression in vivo, However, our analysis of mot1 muta nts shows that, similar to spt3 mutants, they have decreased levels of transcription from certain genes, suggesting that Mot1 may function a s an activator in vivo. In addition, mot1 mutants have other phenotype s in common with spt3 Delta mutants, including suppression of the inse rtion mutation his4-912 delta. Motivated by these Spt3-Mot1 genetic in teractions, we tested for genetic interactions between Spt3 and the ge neral transcription factor TFIIA, TFIIA has been shown previously to b e functionally related to Mot1, We found that overexpression of TFIIA partially suppresses an spt3 Delta mutation, that teal mutants have Sp t(-) phenotypes, and that spt3 Delta teal double mutants are inviable. We believe that, taken together, these data suggest that Spt3, Mot1, and TFIIA cooperate to regulate TBP-DNA interactions, perhaps at the l evel of TATA box selection in vivo.