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A study of Mediator subunit enhancer-promoter binding

ABSTRACT: Mediator is a transcriptional co-activator recruited to enhancers by DNA-binding activators, and it also interacts with RNA polymerase (Pol) II as part of the preinitiation complex (PIC). We demonstrate that a single Mediator complex associates with the enhancer and core promoter in vivo, indicating that it can physically bridge these transcriptional elements. However, the Mediator kinase module associates strongly with the enhancer, but not with the core promoter, and it dissociates from the enhancer upon depletion of the TFIIH kinase. Severing the kinase module from Mediator by removing the connecting subunit Med13 does not affect Mediator association at the core promoter, but increases occupancy at enhancers. Thus, Mediator undergoes a compositional change in which the kinase module, recruited via Mediator to the enhancer, dissociates from Mediator to permit association with Pol II and the PIC. As such, Mediator acts as a dynamic bridge between the enhancer and core promoter.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE82082 | GEO | 2016/10/31

SECONDARY ACCESSION(S): PRJNA323937

REPOSITORIES: GEO

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The Cdk8 kinase module regulates Mediator-RNA polymerase II interaction

Project description:The Cdk8 kinase module (CKM) is a dissociable part of the coactivator complex Mediator that regulates RNA polymerase II (Pol II transcription. The CKM has negative and positive functions in gene transcription that remain poorly understood at the mechanistic level. Here, we prepare recombinant CKM from the yeast Saccharomyces cerevisiae and show that it binds core Mediator (cMed) to sterically inhibit cMed binding to the Pol II preinitiation complex (PIC) in vitro. We further show that the Cdk8 kinase activity of CKM counteracts CKM-cMed interaction,thereby releasing CKM and enabling Mediator to bind the PIC. Finally, we report that the kinase activity of Cdk8 is required for gene activation during heat shock in vivo, but not under steady state growth conditions. These results converge with previous literature on a model for CKM function. In this model, CKM negatively regulates Mediator function at upstream activating sequences by preventing Mediator binding to the PIC at the promoter. During gene activation, Cdk8 kinase activity may release Mediator and allow its binding to the PIC, thereby stimulating transcription initiation and accounting for the positive function of CKM.

2021-06-16 | GSE161140 | GEO

Evidence that Mediator is essential for Pol II transcription but not a required component of the preinitiation complex in vivo

Project description:Mediator, a transcriptional co-activator complex, is recruited to enhancers by DNA-binding activators via its tail module, and it interacts with RNA polymerase (Pol) II as part of the preinitiation complex (PIC) via its head module. Although Mediator has been described as a general transcription factor, it is unclear if it is essential for Pol II transcription and/or is a required component of the PIC in vivo. We comprehensively analyze this issue by measuring Pol II transcription upon rapid depletion of individual or multiple Mediator subunits from the nucleus. Depletion of individual subunits, even those essential for cell growth, causes a general but only modest decrease in Pol II transcription. Transcriptional effects are stronger on SAGA-dependent genes as opposed to TFIID-dependent genes. Thus, Mediator modules that associate either with the enhancer or with the core promoter confer partial transcriptional activity. Furthermore, Pol II transcription can occur when Mediator is not detected at core promoters. In contrast, simultaneous depletion of all Mediator modules causes a drastic decrease in Pol II transcription that is roughly comparable to the effect observed upon anchor-away-mediated depletion of Pol II or TBP. These results provide strong evidence that Mediator is essential for Pol II transcription in vivo, but that it is not a required component of the PIC.

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Structure of Saccharomyces cerevisiae Mediator-RNA polymerase II pre-initiation complex for divergent transcription

Project description:This study has determined structure of transcription initiation complexes including a DNA-bound activator, RNA polymerase II (Pol II), and Mediator on a divergent promoter GAL80/SUT719 using a combination of cryo-EM and XL-MS analyses. Our cryo-EM single-particle analysis reveals a dimeric form of Med-PIC through the Mediator Tail module induced by the activator protein. Density of the upstream DNA bound to the Gal4-VP16 was identifiable along the Mediator Tail module, while XL-MS localized flexible regions that were not visible by cryo-EM analysis, such as activator-binding domains (ABDs and KIX).

2024-05-22 | PXD036149 | Pride

Architectural Mediator subunits are differentially essential for global transcription in yeast (ChIP-seq)

Project description:Mediator is a modular complex required for RNA polymerase II transcription in vivo. We show that Mediator destabilization via depletion of the main complex scaffold Med14 or the head module scaffold Med17 is lethal and results in global transcriptional downregulation, though Med17 destruction has a markedly greater negative effect. Depletion of Med14 or Med17 impairs pre-initiation complex (PIC) formation and/or stability to similar degrees, suggesting that the differential transcriptional effects of head module destabilization and overall dissociation of the complex are not due to different extents of defective PIC formation. Co-depletion of Med14 and Med17 reduced transcription and TFIIB promoter occupancy to similar degrees as Med17 loss alone, suggesting that the independent head module can weakly stimulate transcription in vivo, though not at a level that maintains viability. Collectively, our data suggest that the head is the major functional module of Mediator with respect to PIC function in vivo.

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Structural basis of the human transcriptional Mediator complex modulated by its dissociable Kinase module

Project description:The Mediator complex consists of a Core and a dissociable Kinase module. This project is to understand the binding mode between the Core and Kinase module. Both Mediator complex and its Kinase module were individually crosslinked and analyzed by XL-MS.

2024-11-21 | PXD044328 | Pride

The Pol II Pre-Initiation Complex (PIC) Influences Mediator Binding but Not Promoter-Enhancer Looping [promoter_capture_Hi-C]

Project description:Knowledge of how Mediator and TFIID crosstalk contributes to promoter-enhancer (P-E) communication is important for elucidating the mechanism of enhancer function. We conducted an shRNA knockdown screen in murine embryonic stem cells to identify the functional overlap between Mediator and TFIID subunits on gene expression. Auxin-inducible degrons were constructed for TAF12 and MED4, the subunits eliciting the greatest overlap. Degradation of TAF12 led to a dramatic genomewide decrease in gene expression accompanied by destruction of TFIID, loss of Pol II pre-initiation complex (PIC) at the promoter, and significantly decreased Mediator binding to promoters and enhancers. Interestingly, loss of the PIC elicited only a mild effect on P-E looping by Promoter Capture Hi-C (PCHi-C). Degradation of MED4 had a minor effect of Mediator integrity but led to a consistent 2-fold loss in gene expression, decreased binding of Pol II to Mediator, and decreased recruitment of Pol II to the promoters, but no effect on the other PIC components. PCHi-C revealed no consistent effect of Med4 degradation on P-E looping. Collectively, our data show that TAF12 and MED4 contribute mechanistically in different ways to P-E communication but neither factor appears to directly control P-E looping, thereby dissociating P-E communication from physical looping.

2021-07-22 | GSE178851 | GEO

The Pol II Pre-Initiation Complex (PIC) Influences Mediator Binding but Not Promoter-Enhancer Looping [nascent RNA-seq]

2021-07-22 | GSE178850 | GEO

The Pol II Pre-Initiation Complex (PIC) Influences Mediator Binding but Not Promoter-Enhancer Looping [RNA-seq]

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The Pol II Pre-Initiation Complex (PIC) Influences Mediator Binding but Not Promoter-Enhancer Looping [ChIP-seq]

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