Project description:Disruptions to iron-sulfur (Fe-S) clusters, essential cofactors for a broad range of proteins, cause widespread cellular defects resulting in human disease. An underappreciated source of damage to Fe-S clusters are cuprous (Cu1+) ions. Since histone H3 enzymatically produces Cu1+ to support copper-dependent functions, we asked whether this activity could become detrimental to Fe-S clusters. Here, we report that histone H3-mediated Cu1+ toxicity is a major determinant of cellular functional pool of Fe-S clusters. Inadequate Fe-S cluster supply, either due to diminished assembly as occurs in Friedreich’s Ataxia or defective distribution, causes severe metabolic and growth defects in S. cerevisiae. Decreasing Cu1+ abundance, through attenuation of histone cupric reductase activity or depletion of total cellular copper, restored Fe-S cluster-dependent metabolism and growth. Our findings reveal a novel interplay between chromatin and mitochondria in Fe-S cluster homeostasis, and a potential pathogenic role for histone enzyme activity and Cu1+ in diseases with Fe-S cluster dysfunction.
Project description:Histone acetylation is important for the activation of gene transcription but little is known about its direct ‘read/write’ mechanisms. Here, we report cryo-electron microscopy structures in which a p300/CBP multidomain monomer recognizes histone H4 N-terminal tail (NT) acetylation (ac) in a nucleosome and acetylates non-H4 histone NTs within the same nucleosome. p300/CBP not only recognized H4NTac via the bromodomain pocket responsible for ‘reading’, but also interacted with the DNA minor grooves via the outside of that pocket. This directed the catalytic center of p300/CBP to one of the non-H4 histone NTs. The primary target that p300 ‘writes’ by ‘reading’ H4NTac was H2BNT, and H2BNTac promoted H2A-H2B dissociation from the nucleosome. We propose a model in which p300/CBP ‘replicates’ histone NT acetylation within the H3-H4 tetramer to inherit epigenetic storage, and ‘transcribes’ it from the H3-H4 tetramer to the H2B-H2A dimers to activate context-dependent gene transcription through local nucleosome destabilization.
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:We have performed a comprehensive analysis of the involvement of histone H3 and H4 residues in the regulation of chronological lifespan in yeast. Residues where substitution resulted in the most pronounced lifespan extension are all on the exposed face of the nucleosome, with the exception of H3E50, which is present on the lateral surface, between two DNA gyres. Other residues that had a more modest effect on lifespan extension were concentrated at the extremities of the H3-H4 dimer, suggesting a role in stabilizing the dimer in its nucleosome frame. Residues implicated in a reduced lifespan were buried in the histone handshake motif, suggesting that these mutations destabilize the octamer structure. All residues exposed on the disk and that caused lifespan extension are known to interact with Sir3. We find that substitution of H4K16 and H4H18 cause Sir3 to redistribute from telomeres and silent mating loci to secondary positions, often enriched for Rap1 or Abf1 binding sites, whereas H3E50 does not. The redistributed Sir3 cause transcriptional repression at most of the new loci, including of genes where null mutants were previously shown to extend chronological lifespan. The transcriptomic profiles of H4K16 and H4H18 mutant strains are very similar, and compatible with a DNA replication stress response. This is distinct from the transcriptomic profile of H3E50, which matches strong induction of oxidative phosphorylation. We propose that different clusters of H3 and H4 residues are involved in either binding to non-histone proteins, or in destabilizing the association of the nucleosome DNA, or disrupting binding of a H3-H4 dimer in the nucleosome, or disturbing the structural stability of the octamer, each category impacting on chronological lifespan through a different path.
Project description:We have performed a comprehensive analysis of the involvement of histone H3 and H4 residues in the regulation of chronological lifespan in yeast. Residues where substitution resulted in the most pronounced lifespan extension are all on the exposed face of the nucleosome, with the exception of H3E50, which is present on the lateral surface, between two DNA gyres. Other residues that had a more modest effect on lifespan extension were concentrated at the extremities of the H3-H4 dimer, suggesting a role in stabilizing the dimer in its nucleosome frame. Residues implicated in a reduced lifespan were buried in the histone handshake motif, suggesting that these mutations destabilize the octamer structure. All residues exposed on the disk and that caused lifespan extension are known to interact with Sir3. We find that substitution of H4K16 and H4H18 cause Sir3 to redistribute from telomeres and silent mating loci to secondary positions, often enriched for Rap1 or Abf1 binding sites, whereas H3E50 does not. The redistributed Sir3 cause transcriptional repression at most of the new loci, including of genes where null mutants were previously shown to extend chronological lifespan. The transcriptomic profiles of H4K16 and H4H18 mutant strains are very similar, and compatible with a DNA replication stress response. This is distinct from the transcriptomic profile of H3E50, which matches strong induction of oxidative phosphorylation. We propose that different clusters of H3 and H4 residues are involved in either binding to non-histone proteins, or in destabilizing the association of the nucleosome DNA, or disrupting binding of a H3-H4 dimer in the nucleosome, or disturbing the structural stability of the octamer, each category impacting on chronological lifespan through a different path.
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.