Project description:Histone post-translational modifications (PTMs) alter chromatin structure by promoting the interaction of chromatin-modifying complexes with nucleosomes. The majority of chromatin-modifying complexes contain multiple domains that preferentially interact with modified histones, leading to speculation that these domains function in concert to target nucleosomes with distinct combinations of histone PTMs. In S. cerevisiae, the NuA3 histone acetyltransferase complex contains three domains, the PHD finger in Yng1, the PWWP domain in Pdp3, and the YEATS domain in Taf14, which in vitro bind to H3K4 methylation, H3K36 methylation, and acetylated and crotonylated H3K9 respectively. However the relative in vivo contributions of these histone PTMs in targeting NuA3 is unknown. Here we show that in vivo H4K4 and H3K36 methylation, but not acetylated or crotonylated H3K9, recruit NuA3 to transcribed genes. Through genome-wide colocalization and by mutational interrogation, we demonstrate that the PHD finger of Yng1, and the PWWP domain of Pdp3 independently target NuA3 to H3K4 and H3K36 methylated chromatin respectively. In contrast, we find no evidence to support the YEATS domain of Taf14 functioning in NuA3 recruitment. Collectively our results suggest that the presence of multiple histone-PTM binding domains within NuA3, rather than restricting it to nucleosomes containing distinct combinations of histone PTMs, can serve to increase the range of nucleosomes bound by the complex. Interestingly however, the simple presence of NuA3 is insufficient to ensure acetylation of the associated nucleosomes, suggesting a secondary level of acetylation regulation that does not involve control of HAT-nucleosome interactions.
Project description:Histone lysine methylation is a key epigenetic modification that regulates eukaryotic transcription. In Saccharomyces cerevisiae, it is controlled by a reduced but evolutionarily conserved suite of methyltransferase (Set1p, Set2p, Dot1p, and Set5p) and demethylase (Jhd1p, Jhd2p, Rph1p, and Gis1p) enzymes. Many of these enzymes are extensively phosphorylated in vivo; however, the functions of specific phosphosites are poorly understood. Here, we comprehensively investigate the phosphoregulation of the yeast histone methylation network by analysing 40 phosphosites on six enzymes through mutagenesis. A total of 82 genomically-edited S. cerevisiae strains were generated and screened for changes in native H3K4, H3K36, and H3K79 methylation levels, and for sensitivity to environmental stress conditions. This demonstrated the functional relevance of phosphosites on methyltransferase Set2p (S6, S8, S10, and T127) and demethylase Jhd1p (S44) in the regulation of H3K36 methylation in vivo, and in the coordination of specific stress response pathways in budding yeast. Proteomic analysis of SET2 mutants revealed that phosphorylation site mutations lead to significant downregulation of membrane-associated proteins and processes, consistent with changes brought about by SET2 deletion. This study represents the first systematic investigation into the phosphoregulation of an entire epigenetic network in any eukaryote, and our findings establish phosphorylation as an important regulator of histone lysine methylation in S. cerevisiae.
Project description:Spn1/Iws1 is a conserved protein involved in transcription and chromatin dynamics, yet its general in vivo requirement for these functions is unknown. Using a Spn1 depletion system in S. cerevisiae, we demonstrate that Spn1 broadly influences several aspects of gene expression on a genome-wide scale. We show that Spn1 is globally required for normal mRNA levels and for normal splicing of ribosomal protein transcripts. Furthermore, Spn1 maintains the localization of H3K36 and H3K4 methylation across the genome and is required for normal histone levels at highly expressed genes. Finally, we show that the association of Spn1 with the transcription machinery is strongly dependent on its binding partner, Spt6, while the association of Spt6 and Set2 with transcribed regions is partially dependent on Spn1. Taken together, our results show that Spn1 affects multiple aspects of gene expression in vivo and provide additional evidence that it functions as a histone chaperone.
Project description:Nucleosomes must be deacetylated behind elongating RNA polymerase II to prevent cryptic initiation of transcription within the coding region. RNA polymerase II signals for deacetylation through methylation of histone H3 lysine 36 (H3K36) which provides the recruitment signal for the Rpd3S deacetylase complex. Recognition of methyl-H3K36 by Rpd3S requires the chromodomain of its Eaf3 subunit. Paradoxically, Eaf3 is also a subunit of the NuA4 acetyltransferase complex yet NuA4 does not recognize methyl H3K36 nucleosomes. We found that methyl H3K36 nucleosome recognition by Rpd3S also requires the PHD domain of its Rco1 subunit. Thus, the coupled chromo and PHD domains of Rpd3S specifies recognition of the methyl H3K36 mark; demonstrating the first combinatorial domain requirement within a protein complex to read a specific histone code.
Project description:Histone methylation is central to the regulation of eukaryotic transcription. In Saccharomyces cerevisiae, it is controlled by a system of four methyltransferases (Set1p, Set2p, Set5p, and Dot1p) and four demethylases (Jhd1p, Jhd2p, Rph1p, and Gis1p). While the histone targets for these enzymes are well characterised, the connection of the enzymes with the intracellular signalling network and thus their regulation is poorly understood, in yeast and in all other eukaryotes. Here we report the detailed characterisation of the eight S. cerevisiae enzymes, and show that they carry a total of 75 phosphorylation sites, 93 acetylation sites, and two ubiquitination sites. All enzymes are subject to phosphorylation, although demethylases Jhd1p and Jhd2p contained one and five sites respectively whereas other enzymes carried 14 to 36 sites. Phosphorylation was absent or under-represented on catalytic and other domains but strongly enriched for regions of disorder on methyltransferases, suggesting a role in the modulation of protein-protein interactions. We show that a phosphorylation cluster within an acidic and intrinsically disordered N-terminal region of methyltransferase Set2p regulates H3K36 methylation levels in vivo, thus supporting the functional relevance of disordered phosphosites. While most kinases upstream of the yeast histone methylation enzymes remain unknown, we model the possible connections between the signalling network and the histone-based gene regulatory system and propose an integrated regulatory structure. Our results provide a foundation for future, detailed exploration of the role of specific kinases and phosphosites in the regulation of histone methylation.