engleski

Requirement for chromatin remodeling activities at the yeast PHO84 promoter

The yeast PHO84 promoter, which is coregulated with the well studied PHO5 and PHO8 promoters in response to phosphate availability, is the strongest promoter of the PHO family, containing five binding sites for the specific activator Pho4. Under repressive conditions there is a short hypersensitive region in the promoter containing two closely positioned Pho4 binding sites, but upon induction the promoter chromatin structure is altered, so that at least one nucleosome upstream and one downstream from the hypersensitive region are remodeled. Remodeling of chromatin structure leads to histone depletion from the promoter region. The rate of histone eviction and consequently the rate of promoter activation are strongly delayed in mutants deleted for either Snf2 or Gcn5. Nonetheless, after prolonged induction full activation is achieved, but in the absence of Snf2 chromatin remodeling is only partial, resulting in displacement of the downstream but not of the upstream nucleosome. Therefore, eviction of these two nucleosomes requires different chromatin remodeling activities. In contrast to Snf2, Gcn5 is not required for efficient remodeling of both nucleosomes upon full induction, either in the presence or absence of Snf2. Similarly to Gcn5, the absence of Ino80 also causes delay in the promoter activation without affecting the final extent of chromatin remodeling and the same is true for the histone chaperone Asf1. Taken together, Gcn5, Ino80, or Asf1 affects only the rate of remodeling at the PHO84 promoter, similar as we previously found for the PHO5 promoter. However, with respect to the requirement for Snf2, the PHO84 promoter chromatin structure possesses hybrid characteristics compared to the two coregulated promoters: the PHO8 is essentially dependent on Snf2 and at the PHO5 only the rate of chromatin remodeling is reduced in the absence of Snf2. We have also examined a possible role of the histone variant H2A.Z in regulation of chromatin remodeling at PHO promoters. Interestingly, the absence of H2A.Z has only a slight effect on activation of the PHO5 promoter, but causes a strong delay in the activation kinetics of the PHO84 promoter. This provides additional evidence that chromatin remodeling process at the two coregulated promoters involves different mechanisms.

chromatin remodeling; yeast PHO84 promoter; transcriptional regulation

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