Genetic and biochemical studies of Adr6, a component of the SWI /SNF chromatin remodeling complex

The remodeling of chromatin plays an important role in gene transcription in eukaryotes. The SWI/SNF complex in Saccharomyces cerevisiae is composed of 11 distinct proteins that together remodel histones in an ATP dependent manner. One member of this complex, encoded by the ADR6 (SWI1) gene in S. cerevisiae, is a positive regulator of transcription at the ADH2 locus. The two main goals of this research were first to identify the elements within the ADH2 promoter required for the targeting of SWI/SNF, and second to determine the specific role of Adr6 within the SWI/SNF complex. Research from several labs has found that transcription factors serve to recruit SWI/SNF to promoter regions. To investigate targeting at ADH2, studies of both its primary transcription factor, ADR1, and other promoter elements were carried out. In an initial set of experiments, we found that a mini-ADR1 gene containing only the primary activation domain was dependent on Adr6. If Adr1 were serving to recruit SWI/SNF, then one would expect that alterations in the activation might affect Adr6 dependence. In subsequent studies we found that mutations in this activation domain on mini-Adr1 did not significantly alter the Adr6 dependence. Alternatively, ADH2 expression may be affected by SWI/SNF indirectly. We next examined the role of different regions within the ADH2 promoter in conferring Adr6 dependence. We found that neither the UAS2 region nor the poly-A tract played a significant role in targeting of SWI/SNF to ADH2. These results suggest that an alternative form of recruitment of SWI/SNF may be at play at the ADH2 locus. To examine the specific role of Adr6 within the SWI/SNF complex, a deletion analysis of the Adr6 protein was carried out. We found that the C-terminal half of the protein is required for function. Further, biochemical studies of deletion mutants within this region suggested that each retains its ability to enter the SWI/SNF complex. These results indicate that the C-terminal region of Adr6 may play an important structural role within the complex, or in mediating interactions with proteins outside the complex.