Regulated Displacement of TBP from the PHO8 Promoter In Vivo Requires Cbf1 and the Isw1 Chromatin Remodeling Complex

Abstract

Regulated binding of TBP to a promoter is a key event in transcriptional regulation. We show here that on glucose depletion, the S. cerevisiae Isw1 chromatin remodeling complex is required for the displacement of TBP from the PHO8 promoter. Displacement of TBP also requires the sequence-specific bHLH-LZ factor Cbf1p that targets Isw1p to the PHO8 UAS. Cbf1p- and Isw1p-dependent displacement of TBP is also observed at the PHO84 promoter, but not at the ADH1 promoter, where loss of TBP is Cbf1p- and Isw1p independent. The results point to a promoter-specific Isw1p-dependent mechanism for targeted regulation of basal transcription by displacement of TBP from a promoter.

Cbf1p Is Required for Chromatin Remodeling at Promoter-proximal CACGTG Motifs in Yeast

“…A physical association between Cbf1p and the chromatin remodeling ATPase Isw1p has been shown recently at the PHO8 locus (30), suggesting that the nucleosome sliding activity of the Isw1p enzyme is directly recruited by Cbf1p to modulate chromatin structure. We have shown here that Cbf1p also appears to recruit Isw1p to the DRS2 upstream region.…”

“…Transcript levels at PGK became moderately elevated in the absence of Cbf1p (34). Many other genes, such as GAL2, TRP1, CYT1, RPL45, QCR8, GSH1, and PHO8 showed similar slight perturbation of transcript levels either positively or negatively (19,32,33,(35)(36)(37)30). We envisage that Cbf1p acts as a contextdependent transcription factor with the importance of its role depending on the types of interactions made with other transacting factors and the underlying nucleosomal environment.…”

“…However, they do not address the mechanism by which Cbf1p modulates chromatin structure. It has recently been shown that both Cbf1p and the chromatin-remodeling ATPase Isw1p are required for repression of the PHO8 gene (which contains a single CACGTG motif at Ϫ534bp) and that Cbf1p functions to recruit the Isw1p complex to PHO8 DNA (30). It has also been shown that both Isw1p itself and Isw1p-dependent chromatin structures are present at the Cbf1p-bound MET16 and DRS2 promoter regions (40,52).…”

“…This function is likely to involve the recruitment of the chromatin remodeling ATPase Isw1p (30). Although the chromatin-remodeling function of Cbf1p is not absolutely required for MET gene activation, it appears to influence the kinetics of activation (20).…”

Chromatin Remodeling Factors Isw2 and Ino80 Regulate Checkpoint Activity and Chromatin Structure in S Phase

“…Isw2 has the ability to translocate on ssDNA (Fischer et al 2009). Furthermore, chromatin remodeling factors have been shown to interact with nonhistone proteins, and Mot1, an ATPase that is highly related to chromatin remodeling factors, can displace TBP, a nonhistone protein, from DNA (Auble et al 1994;Moreau et al 2003;Au et al 2011;Sugimoto et al 2011). Because Isw2 and Ino80 physically interact with RPA (Au et al 2011), we initially considered the possibility that they may be able to directly remove RPA from the ssDNA template using DNA translocase activity.…”