Project description:Mediator is a highly conserved transcriptional coactivator organized into four modules, namely Tail, Middle, Head and Kinase (CKM). Previous work suggests regulatory roles for Tail and CKM, but an integrated model for these activities is lacking. Here, we analyzed the genome-wide distribution of Mediator subunits in wild-type and mutant yeast cells in which RNA polymerase II promoter escape is blocked allowing detection of transient Mediator forms. We found that while all modules are recruited to upstream activated regions (UAS), assembly of Mediator within the pre-initiation complex is accompanied by the release of CKM. Surprisingly, our data show that CKM regulates Mediator-UAS interaction rather than Mediator-promoter association. In addition, while Tail is required for Mediator recruitment to UAS, Tail-less Mediator nevertheless interacts with core promoters. Collectively, our data suggest that the essential function of Mediator is mediated by Head and Middle at core promoters, while Tail and CKM play regulatory roles.

2016-10-20 | GSE81127 | GEO

Tail and Kinase Modules Differently Regulate Core Mediator Recruitment and Function In Vivo

Project description:Mediator is a highly conserved transcriptional coactivator organized into four modules, namely Tail, Middle, Head and Kinase (CKM). Previous work suggests regulatory roles for Tail and CKM, but an integrated model for these activities is lacking. Here, we analyzed the genome-wide distribution of Mediator subunits in wild-type and mutant yeast cells in which RNA polymerase II promoter escape is blocked allowing detection of transient Mediator forms. We found that while all modules are recruited to upstream activated regions (UAS), assembly of Mediator within the pre-initiation complex is accompanied by the release of CKM. Interestingly, our data show that CKM regulates Mediator-UAS interaction rather than Mediator-promoter association. In addition, while Tail is required for Mediator recruitment to UAS, Tail-less Mediator nevertheless interacts with core promoters. Collectively, our data suggest that the essential function of Mediator is mediated by Head and Middle at core promoters, while Tail and CKM play regulatory roles.

2016-10-25 | GSE81107 | GEO

Kin28 Regulates the Transient Association of Mediator with Core Promoters

Project description:Mediator is an essential, broadly utilized eukaryotic transcriptional co-activator. How and what it communicates from activators to RNA polymerase II remains an open question. Here we performed genome-wide location profiling of yeast Mediator subunits. Mediator is not found at core promoters but rather occupies the upstream activating sequence (UAS), upstream of the pre-initiation complex. In the absence of Kin28/CDK7 kinase activity, or in cells where the CTD is mutated to replace Ser5 with alanines, however, Mediator accumulates at core promoters together with RNAPII. We propose that Mediator is quickly released from promoters upon Ser5 phosphorylation by Kin28/CDK7, which also allows for RNAPII to escape from the promoter. We took a systematic approach to examine the genome-wide distribution (using ChIP-chip) of the various Mediator subunits. Mediator occupancy was also assayed in mutants for most of the CTD kinases and in strains where some CTD serines had been replaced by alanines. Mediator ChIPs were performed with Myc-tagged subunits, except in some preliminary experiments where polyclonal antibodies were used. Most ChIPs (in Cy5) were hybridyzed against a control ChIP sample from an isogenic non-tagged strain (in Cy3). In some of the preliminary experiments, non immunoprecipitated DNA (input) was used as the control. In addition to Mediator ChIPs, the project includes TFIIB and RNAPII (Rpb3) ChIP-chip datasets. All ChIP-chip experiments were done in duplicates except for the preliminary experiments that were done in monoplicat for the most part. Each microarray was normalized using the Lima Loess and replicates were combined using a weighted average method as previously described (Pokholok et al., 2005).

2014-03-24 | E-GEOD-55402 | biostudies-arrayexpress

ChIP-seq of Mediator subunits in Mediator mutants and wild type yeast

Project description:Mediator subunits Med17 (Srb4) and Med15 (Gal11) were subjected to ChIP in wild type yeast, med18 (srb5), med20 (srb2), and med2 med3 med15 (triple mutant) yeast, all in kin28-anchor away yeast after 1 hr rapamycin treatment to evict Kin28 from the nucleus. This results in inactivation of Kin28, which reduces Mediator turnover at promoters and allows stronger Mediator ChIP signal at promoters. <br></br>Both Med17 and Med15 were tagged with myc and precipitated using the monoclonal antibody against c-myc. Please note that a specific control for rapamycin treatment was not performed in this experiment, as that has been well documented in the literature for this experiment, using what is called the anchor away method. The untagged sample is a control for non-specific immunoprecipitation.

2017-12-01 | E-MTAB-5824 | biostudies-arrayexpress

MEDIATOR subunit med8 binding in Saccharomyces cerevisiae

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.

2011-11-22 | GSE28613 | GEO

Saccharomyces cerevisiae

Project description:Core Mediator structure at 3.4 A extends transcription initiation complex model

| PRJNA377258 | ENA

MEDIATOR subunit med8 binding in Saccharomyces cerevisiae

2011-11-22 | E-GEOD-28613 | biostudies-arrayexpress

Saccharomyces cerevisiae

Project description:A library of native and synthetic yeast core promoters driving YFP expression

| PRJNA281926 | ENA