Project description:The MYST HAT Sas2 is part of the SAS-I complex. The target for acetylation by Sas2 is Lys16 of histone H4 (H4 K16Ac). This acetylation site marks euchromatic regions and opposes the spreading of heterochromatin at telomere-proximal regions. Changes of SAS-I-mediated H4 K16Ac on a genome-wide scale comparing wt and sas2∆ cells were investigated in this study. We found a pronounced, genome-wide loss of H4 K16 acetylation in the body of transcribed genes in the absence of Sas2. Furthermore, the influence of Sas2 on gene expression was investigated in RNA expression arrays.
Project description:The MYST HAT Sas2 is part of the SAS-I complex. The target for acetylation by Sas2 is Lys16 of histone H4 (H4 K16Ac). This acetylation site marks euchromatic regions and opposes the spreading of heterochromatin at telomere-proximal regions. Changes of SAS-I-mediated H4 K16Ac on a genome-wide scale comparing wt and sas2M-bM-^HM-^F cells were investigated in this study. We found a pronounced, genome-wide loss of H4 K16 acetylation in the body of transcribed genes in the absence of Sas2. Furthermore, the influence of Sas2 on gene expression was investigated in RNA expression arrays. H4 K16Ac and H4 in wt and sas2M-bM-^HM-^F was ChIPed. ChIP experiments were performed three times with independent chromatin preparations.
Project description:The histone acetyltransferase Sas2 is part of the SAS-I complex and acetylates lysine 16 of histone H4 (H4 K16Ac) in the genome of Saccharomyces cerevisiae. Sas2-mediated H4 K16Ac is strongest over the coding region of genes with low expression. However, it is unclear how Sas2-mediated acetylation is incorporated into chromatin. Our previous work has shown physical interactions of SAS with the histone chaperones CAF-I and Asf1, suggesting a link between SAS-I mediated acetylation and chromatin assembly. Here, we find that Sas2-dependent H4 K16Ac in bulk histones requires passage of the cells through the S-phase of the cell cycle, and the rate of increase in H4 K16Ac depends on both CAF-I and Asf1, whereas steady-state levels and genome-wide distribution of H4 K16Ac shows only mild changes in their absence. Furthermore, H4 K16Ac is deposited in chromatin at genes upon repression, and this deposition requires the histone chaperone Spt6, but not CAF-I, Asf1, HIR or Rtt106. Altogether, our data indicate that Spt6 controls H4 K16Ac levels by incorporating K16-unacetylated H4 in strongly transcribed genes. Upon repression, Spt6 association is decreased, resulting in less deposition of K16-unacetylated and therefore in a concomitant increase of H4 K16Ac that is recycled during transcription.
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.
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. Med8-TAP strain ChIPed with IgG beads vs. Input in Saccharomyces cerevisiae
Project description:Changes in acetylation of histone H4 are a common hallmark of cancer cells. In leukemia cells, histone H4 is characterized by loss of K16 mono-acetylation. Bromodomain proteins specifically recognize acetylated lysines and have been used as a target for anti cancer drug, JQ1 and iBET. Although acetylation and de-acetylation of histone H4 have been shown to have big impact in cancer cells, little attention has been focused on histone H4-acetylation at a genome level. To uncover potential epigenetic role of hyper-acetylated histone H4 at a genome-wide level in cancer cell, we generated a novel monoclonal antibody specifically recognizing histone H4 with at least two acetylated lysine residues (H4K5ac+K8ac). At the genome-wide level, hyper-acetylated histone H4 is associated with promoter and regulatory element (active enhancer, eRNA and super enhancer). We show that diacetylation at K5 and K8 of histone H4 co-localizes H3K27ac and BRD2 in the majority of active enhancer and promoters. However BRD2 has a stronger association with H4K5acK8ac. Furthermore we identified two specific chromatin states, which separately contain either H3K27ac or acetylated histone H4. Although JQ1 led to global reduction of BRD2 binding on the chromatin, only local changes of histone H4 multi-acetylation were observed upon BET inhibition by JQ1
Project description:Specific histone modifications play important roles in chromatin functions such as activation or repression of gene transcription. These participation must occur as a dynamic process, however, most of histone modification state maps reported to date only provide static pictures linking certain modification with active or silenced states. This study focused on the global histone modification variation that occurs in response to transcriptional reprogramming produced by a physiological perturbation in yeast. We have performed genome-wide chromatin immunoprecipitation analysis for eight specific histone modifications before and after of a saline stress. The most striking change is a quick deacetylation of lysines 9 and 14 of H3 and lysine 8 of H4 associated to repression of genes. Genes that are activated increase the acetylation levels at these same sites, but this acetylation process of activated genes seems minor quantitatively to that of the deacetylation of repressed genes. The observed changes in tri-methylation of lysines 4, 36 and 79 of H3 and also di-methylation of lysine 79 of H3 are much more moderate than those of acetylation. Additionally, we have produced new genome-wide maps for six histone modifications at more than five times higher resolution of previous available data and analyzed for the first time in S. cerevisiae genome wide profiles of two more, acetylation of lysine 8 of H4 and di-methylation of lysine 79 of H3. In this research we have shown that dynamic of acetylation state of histones during activation or repression of transcription is a process much quicker than methylation and therefore the changes produced in the acetylation may affect methylation but the reverse path is not possible.
Project description:Specific histone modifications play important roles in chromatin functions such as activation or repression of gene transcription. These participation must occur as a dynamic process, however, most of histone modification state maps reported to date only provide static pictures linking certain modification with active or silenced states. This study focused on the global histone modification variation that occurs in response to transcriptional reprogramming produced by a physiological perturbation in yeast. We have performed genome-wide chromatin immunoprecipitation analysis for eight specific histone modifications before and after of a saline stress. The most striking change is a quick deacetylation of lysines 9 and 14 of H3 and lysine 8 of H4 associated to repression of genes. Genes that are activated increase the acetylation levels at these same sites, but this acetylation process of activated genes seems minor quantitatively to that of the deacetylation of repressed genes. The observed changes in tri-methylation of lysines 4, 36 and 79 of H3 and also di-methylation of lysine 79 of H3 are much more moderate than those of acetylation. Additionally, we have produced new genome-wide maps for six histone modifications at more than five times higher resolution of previous available data and analyzed for the first time in S. cerevisiae genome wide profiles of two more, acetylation of lysine 8 of H4 and di-methylation of lysine 79 of H3. In this research we have shown that dynamic of acetylation state of histones during activation or repression of transcription is a process much quicker than methylation and therefore the changes produced in the acetylation may affect methylation but the reverse path is not possible. The experiments described in this study compare ChIP with a histone modification antibody to a control ChIP with a core histone antibody. Budding yeast samples were analyzed in exponential growing conditions (YPD) or after 10 minutes of 0.4M NaCl stress. For each experiment 1 or 2 biological replicates were performed.