Project description:Total RNA samples from three replicate cultures of wild type and mutant yeast strains was isolated and expression profile done using Affymetrix arrays. Comparsion between the samples indicate how mutation in a single amino acid residue in histone H4 (H4R45H) affects gene expression in yeast. Such a mutation in histone H4 is known to generate a specific class of mutants called SWI/SNF independent (SIN) mutants, and the mutants were identified by their ability to carry out transcription in the absence of yeast chromatin remodeling complex SWI/SNF. SIN mutations are known to affect higher order chromatin structure and the comparative expression profile would help identification of genes which get affected by such altered chromatin landscape. Keywords: mutant analysis
Project description:The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. Genome wide localization studies have demonstrated that Mediator occupancy not only correlates with high levels of transcription, but that the complex also is present at transcriptionally silenced locations. We provide evidence that Mediator localization is guided by an interaction with histone tails, and that this interaction is regulated by their post-translational modifications. A quantitative, high-density genetic interaction map revealed links between Mediator components and factors affecting chromatin structure, especially histone deacetylases. Peptide binding assays demonstrated that pure wild type Mediator forms stable complexes with the tails of Histone H3 and H4. These binding assays also showed Mediator – histone H4 peptide interactions are specifically inhibited by acetylation of the histone H4 lysine 16, a residue critical in transcriptional silencing. Finally, these findings were validated by tiling array analysis, that revealed a broad correlation between Mediator and nucleosome occupancy in vivo, but a negative correlation between Mediator and nucleosomes acetylated at histone H4 lysine 16. Our studies show that chromatin structure and the acetylation state of histones are intimately connected to Mediator localization.