MED26

Mediator of RNA polymerase II transcription subunit 26 is an is_associated_with::enzyme that in humans is encoded by the MED26 is_associated_with::gene. It forms part of the Mediator complex.

Activity
MED26 or is_associated_with::Transcription factor IIS (TFIIS) is a transcription is_associated_with::elongation factor that increases the overall transcription rate of RNA is_associated_with::polymerase II by reactivating transcription elongation complexes that have arrested transcription. It does this through recruiting ELL/EAF- and P-TEFb- containing complexes to promoters via a direct interaction with the N-terminal domain (NTD). The MED26 NTD also binds TFIID, and TFIID and elongation complexes interact with MED26 through overlapping binding sites. MED26 NTD may function as a molecular switch contributing to the transition of Pol II into productive elongation.

The three is_associated_with::structural domains of TFIIS are conserved from yeast to human. The 80 or so N-terminal residues form a is_associated_with::protein interaction domain containing a conserved motif, which has been called the LW motif because of the invariant is_associated_with::leucine and is_associated_with::tryptophan residues it contains. Although the N-terminal domain is not needed for transcriptional activity, a similar sequence has been identified in other is_associated_with::transcription factors and is_associated_with::proteins that are predominantly nuclear localized,:


 * MED26 (also known as CRSP70 and ARC70), a subunit of the Mediator complex, which is required for the activity of the enhancer-binding protein Sp1.


 * Elongin A, a subunit of a transcription elongation factor previously known as SIII. It increases the rate of transcription by suppressing transient pausing of the elongation complex.


 * PPP1R10, a nuclear regulatory subunit of protein is_associated_with::phosphatase 1 that was previously known as p99, FB19 or PNUTS.


 * PIBP, a small hypothetical protein that could be a phosphoinositide binding protein.


 * IWS1, which is thought to function in both is_associated_with::transcription initiation and elongation. The TFIIS N-terminal domain is a compact four-helix bundle. The is_associated_with::hydrophobic core residues of helices 2, 3, and 4 are well conserved among TFIIS domains, although is_associated_with::helix 1 is less conserved.

Interactions
MED26 has been shown to interact with is_associated_with::MED8, is_associated_with::Cyclin-dependent kinase 8, is_associated_with::POLR2A, is_associated_with::MED12 and is_associated_with::MED28. It also acts synergistically to mediate the interaction between REST (a Kruppel-type zinc finger transcription factor that binds to a 21-bp RE1 silencing element present in over 900 human genes) and Mediator.