engleski

Requirements for chromatin remodeling activities in activation of the yeast PHO84 promoter

We have investigated remodeling of the chromatin structure at the yeast PHO84 promoter, containing five binding sites for the specific activator Pho4, which is the strongest promoter of the PHO family regulated by the phosphate availibility. Under repressive conditions there is a short hypersensitive region in the promoter, containing two closely positioned Pho4 binding sites. Upon induction at least one nucleosome upstream and one downstream from the hypersensitive region are remodeled. This way two additional Pho4 binding sites become accessible. We found that the rate of chromatin remodeling and subsequent promoter activation were strongly delayed in mutants deleted for Snf2, Gcn5 or the Asf1. Nonetheless, after prolonged induction full remodeling was achieved in the absence of Gcn5 or Asf1. However, in the absence of Snf2 remodeling remained only partial. Therefore, the PHO84 promoter shows intermediary dependence on Snf2 compared to the two other coregulated promoters. Whereas the PHO5 promoter chromatin structure can be fully remodeled in the absence of Snf2, remodeling at the PHO8 promoter is strictly dependent on Snf2. By mutating individual Pho4 binding sites promoter derivatives of decreased strength were obtained and requirements for chromatin opening at these promoters were examined. In all cases the mutations did not affect the chromatin transition pattern in a wild type background, but promoter variants with decreased strength showed much stronger dependence on all chromatin modifying activities tested.

chromatin remodeling; yeast PHO84 promoter; transcriptional regulation

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