core mediator complex

Definition

Target type: cellularcomponent

A protein complex that interacts with the carboxy-terminal domain of the largest subunit of RNA polymerase II and plays an active role in transducing the signal from a transcription factor to the transcriptional machinery. The core mediator complex has a stimulatory effect on basal transcription, and contains most of the same subdomains as the larger form of mediator complex -- a head domain comprising proteins known in Saccharomyces as Srb2, -4, and -5, Med6, -8, and -11, and Rox3 proteins; a middle domain comprising Med1, -4, and -7, Nut1 and -2, Cse2, Rgr1, Soh1, and Srb7 proteins; and a tail consisting of Gal11p, Med2p, Pgd1p, and Sin4p -- but lacks the regulatory subcomplex comprising Ssn2, -3, and -8, and Srb8 proteins. Metazoan core mediator complexes have similar modular structures and include homologs of yeast Srb and Med proteins. [PMID:11454195, PMID:16168358, PMID:17870225]

The core mediator complex is a large multi-protein complex that plays a crucial role in regulating gene transcription in eukaryotes. It acts as a bridge between transcription factors and RNA polymerase II, facilitating the initiation and regulation of gene expression. The core mediator complex is composed of several distinct modules, each with specific functions. These modules include:

**Head module:** This module is responsible for interacting with transcription factors and mediating their activation signals. It contains proteins such as MED1, MED17, and MED23.

**Middle module:** This module interacts with RNA polymerase II and is involved in the recruitment and stabilization of the polymerase at the promoter. It contains proteins such as MED4, MED5, and MED6.

**Tail module:** This module interacts with the C-terminal domain (CTD) of RNA polymerase II and is involved in regulating the elongation phase of transcription. It contains proteins such as MED12, MED13, and MED14.

**Kinase module:** This module contains the CDK8 kinase, which phosphorylates specific residues on the CTD of RNA polymerase II, impacting the transition from initiation to elongation.

**Mediator complex assembly:** The core mediator complex is assembled through a hierarchical process involving interactions between its individual modules. The head module serves as a scaffold for the assembly of other modules. The middle and tail modules are recruited to the head module through interactions with specific proteins. The kinase module can associate with the core mediator complex in a regulated manner.

**Functional significance:** The core mediator complex is essential for the proper regulation of gene expression. It plays a critical role in:

* **Transcription initiation:** By bridging transcription factors and RNA polymerase II, the mediator complex facilitates the formation of the pre-initiation complex (PIC).
* **Transcription elongation:** The mediator complex can modulate the elongation phase of transcription through interactions with the CTD of RNA polymerase II.
* **Transcription termination:** The mediator complex can also participate in the termination of transcription by influencing the release of RNA polymerase II from the DNA template.
* **Signal transduction:** The mediator complex can integrate signals from various cellular pathways, including growth factor signaling, stress response, and developmental pathways.

In summary, the core mediator complex is a complex and highly dynamic multi-protein complex that plays a central role in regulating gene transcription in eukaryotes. It acts as a molecular bridge between transcription factors and RNA polymerase II, integrating signals from various cellular pathways and facilitating the precise control of gene expression.'
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Proteins (2)

Compounds (2)