Transcriptional repression of the yeast CHA1 gene requires the chromatin-remodeling complex RSC

Abstract
In eukaryotes, DNA is packaged into chromatin, a compact structure that must be disrupted when genes are transcribed by RNA polymerase II. For transcription to take place, chromatin is remodeled via nucleosome disruption or displacement, a fundamental transcriptional regulatory mechanism in eukaryotic organisms. Here we show that the yeast chromatin‐remodeling complex, RSC (remodels the structure of chromatin), isolated on the basis of homology to the SWI/SNF complex, is required for proper transcriptional regulation and nucleosome positioning in the highly inducible CHA1 promoter. In the absence of Sth1p/Nps1p (a homolog of Swi2p/Snf2p) or of Swh3p (a homolog of Swi3p), expression of CHA1 in non‐induced cells is increased to a level comparable with that of fully induced cells. Furthermore, in non‐induced cells depleted for Sth1p/Nps1p or Swh3p, a nucleosome positioned over the TATA box of the CHA1 promoter is disrupted, an architectural change normally only observed during transcriptional induction. In addition, deletion of the gene‐specific activator Cha4p did not affect derepression of CHA1 in cells depleted for Swh3p. Thus, CHA1 constitutes a target for the RSC complex, and we propose that RSC is essential for maintaining a repressive chromatin structure at the CHA1 promoter.