engleski

How Chromatin Is Remodeled In Vivo

We are investigating the regulation of the PHO5 gene which encodes a strongly regulated acid phosphatase in S. cerevisiae. In these studies we are focusing on the contribution of histone-DNA interactions to gene regulation and the interplay between transcription factors and nucleosome structure. The chromatin structure of the PHO5 promoter undergoes a massive transition upon induction of the gene in the course of which four nucleosomes are disrupted. A transactivating basic-helix-loop-helix protein, Pho4, and a homeodomain protein Pho2 are responsible for the activation of PHO5 and the chromatin transition. The role of Pho2 had remained elusive in the past, and we have now established that it binds cooperatively with Pho4 to the promoter increasing both the affinity of Pho4 for its binding sites and its transactivation potential. In the transition from closed to open chromatin, we can define three distinct states: the fully repressed promoter with positoned nucleosomes, a state with localized nucleosomal perturbations around factor binding sites and the fully open structure with four disrupted nucleosomes. The contribution of the histone acetylase Gcn5 to the activation of PHO5 as well as PHO8, the gene for a regulated alkaline phosphatase, was determined. The precise role of Gcn5 will be discussed.

Chromatin remodeling; transcriptional regulation; PHO5; Saccharomyces cerevisiae

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