PgmNr Y3094: Nucleosomes Are Essential for Proper Regulation of a Multigated Promoter in Saccharomyces cerevisiae.

Authors:
Robert Yarrington; Jenna Goodrum; David Stillman


Institutes
University of Utah, Salt Lake City, UT.


Keyword: Chromatin

Abstract:

We have previously shown that transcription factor binding at HO follows a temporal cascade, with SBF bound at the left half of URS2 (URS2-L) serving to relay a signal from upstream chromatin changes at URS1 to the SBF bound at the right-half of URS2 (URS2-R) that ultimately activate gene expression. We show here that proper nucleosomal context of the URS2 promoter region is essential for this complex transcriptional regulation. Chromatin at the yeast HO promoter is highly repressive and numerous coactivators are required for expression. We modified the HO promoter with segments from the well-studied CLN2 nucleosome-depleted region (NDR), creating chimeric promoters differing in nucleosome occupancy but with binding sites for the same activator, SBF. Nucleosome depletion resulted in substantial increases in both factor binding and gene expression and allowed activation from a much longer distance, presumably by allowing coactivators recruited at the upstream URS1 region to act further downstream. Nucleosome depletion also affected sequential activation of the HO promoter, resulting in promoters no longer requiring both URS1 and URS2-L, as either regulatory region alone is now sufficient to promote binding of the SBF factor to URS2-R. Furthermore, nucleosome depletion at URS2 altered the timing of HO expression and bypassed the regulation that normally restricts expression to mother cells. Our results reveal insight into how nucleosomes can create a requirement for ordered recruitment of factors to facilitate complex transcriptional regulation.



Yeast Database Genetic Index
1. gene symbol: HO; systematic name: YDL227C
2. gene symbol: CLN2; systematic name: YPL256C