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 use biochemically reconstituted transcription initiation components including the Mediator core and Cdk8 kinase modules (CKM) to investigate the function of the CKM in regulating the Mediator-RNA polymerase II interaction in a highly purified system. We use cross-linking coupled to mass spectrometry to map the interaction of the CKM and core Mediator, and in vitro phosphorylation assays followed by phosphopeptide enrichment coupled to mass spectrometry to identify Cdk8 phosphorylation targets in this context and biochemically dissect their functions. Finally, we investigate the function of phosphorylation by Cdk8 on transcription in vivo. Based on that, we propose a model to integrate the phosphorylation-dependent and -independent functions of the CKM in transcription initiation.
Project description:Dynamic 3' UTRs variation mediated by APA is one of the major determinants of post-transcriptional regulation. Though some progress has been made in understanding its function in mammalian cells, the role of APA in the model organism S. cerevisiae, which lack of miRNAs, is a matter of debate. Unlike mammalian cells, most of S. cerevisiae genes tend to express mRNAs with longer 3′ UTRs in proliferating cells. Further analysis demonstrated that 3' UTRs length and mRNA expression were negatively correlated in different growth conditions. By combining APA sequencing and polysome profiling, we observed that mRNA isoforms with shorter 3' UTRs with a higher translational efficiency in proliferating cells but not quiescent. Further analysis demonstrated that different function genes translational efficiency control by APA are differential modulated and closely related with growth conditions. Furthermore, we observed the correlation between asRNAs and translational efficiency of different length 3′ UTR transcripts, suggests asRNAs may involve in the regulation of translational efficiency mediated by APA. Thus, this study indicates conservation of molecular function of APA in different Eukaryotes, highlighting the importance of APA in regulating gene function.
Project description:The ring-like cohesin complex plays an essential role in chromosome segregation, organization, and double-strand break repair through its ability to bring two DNA double helices together. Scc2 (NIPBL in humans) together with Scc4 function as the loader of cohesin onto chromosomes. Chromatin adapters such as the RSC complex facilitate localization of the Scc2-Scc4 cohesin loader. Here we identify a broad range of Scc2- chromatin protein interactions that are evolutionarily conserved and reveal a role for one complex, Mediator, in recruitment of the cohesin loader. We identified budding yeast Med14, a subunit of the Mediator complex, as a high copy suppressor of poor growth in Scc2 mutant strains. Physical and genetic interactions between Scc2 and Mediator are functionally substantiated in direct recruitment and cohesion assays. Depletion of Med14 results in defective sister chromatid cohesion and decreased binding of Scc2 at RNA Pol II transcribed genes. Previous work has suggested that Mediator, Nipbl, and cohesin connect enhancers and promoters of active mammalian genes. Our studies suggest an evolutionarily conserved fundamental role for Mediator in direct recruitment of Scc2 to RNA pol II transcribed genes. We identified two mutations in the evolutionarily conserved HEAT domain of SCC2 that result in significantly reduced growth, scc2R787G and scc2G1242V. This experiment uses ChIP Seq to examine global localization of Scc2 in the presence or absence of MED14.