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 mediator complex is required for activation of transcription of most protein-coding genes, but can also act as a transcriptional corepressor. The Saccharomyces complex contains several identifiable subcomplexes: a head domain comprising 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; a tail consisting of Gal11p, Med2p, Pgd1p, and Sin4p; and a regulatory subcomplex comprising Ssn2, -3, and -8, and Srb8 proteins. Metazoan mediator complexes have similar modular structures and include homologs of yeast Srb and Med proteins. [PMID:11454195, PMID:16168358, PMID:17870225]

The mediator complex is a large multiprotein complex that acts as a bridge between transcription factors and RNA polymerase II. It plays a crucial role in regulating gene expression by integrating signals from various regulatory pathways and facilitating the assembly of the pre-initiation complex at gene promoters. The complex is highly conserved across eukaryotes and comprises 26 subunits in yeast and approximately 30 subunits in mammals. These subunits are organized into four distinct modules: head, middle, tail, and kinase.

The **head module** is the largest and most structurally defined module, containing the subunits Med1, Med17, Med21, Med26, Med14, Med15, Med20, and Med16. This module is responsible for interacting with RNA polymerase II and other general transcription factors. It also contains the Cdk8 module, which is a kinase module that can phosphorylate the C-terminal domain (CTD) of RNA polymerase II and other transcription factors.

The **middle module** is located between the head and tail modules and contains the subunits Med8, Med9, Med10, Med11, Med12, Med13, and Med18. This module interacts with the tail module and plays a crucial role in mediating the recruitment of the mediator complex to gene promoters. It is also involved in integrating signals from various regulatory pathways, including signaling pathways related to stress, cell growth, and development.

The **tail module** is the most variable module, containing subunits Med4, Med5, Med6, Med7, and Med23. This module interacts with transcription factors and other regulatory proteins, facilitating the recruitment of the mediator complex to specific gene promoters. It also contains the cyclin-dependent kinase 8 (CDK8) module, which is a kinase module that can phosphorylate the CTD of RNA polymerase II and other transcription factors.

The **kinase module**, which is part of the head module, contains the subunits Med13, Med14, Med15, and Med16. This module is responsible for phosphorylating the CTD of RNA polymerase II, which is essential for the initiation and elongation of transcription.

The mediator complex functions as a platform for integrating various regulatory signals and coordinating the assembly of the pre-initiation complex at gene promoters. It plays a critical role in regulating gene expression, ensuring that the correct genes are transcribed at the appropriate time and place. The complex is highly dynamic and can undergo conformational changes to regulate its interaction with different transcription factors and other regulatory proteins. This dynamic nature allows the mediator complex to fine-tune gene expression in response to a wide range of cellular signals.'
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Proteins (7)

Compounds (224)