MED26

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

The activation of gene transcription is a multistep process that is triggered by factors that recognize transcriptional enhancer sites in DNA. These factors work with co-activators to direct transcriptional initiation by the RNA polymerase II apparatus. The protein encoded by this gene is a subunit of the CRSP (cofactor required for SP1 activation) complex, which, along with TFIID, is required for efficient activation by SP1. This protein is also a component of other multisubunit complexes e.g. thyroid hormone receptor-(TR-) associated proteins which interact with TR and facilitate TR function on DNA templates in conjunction with initiation factors and cofactors.

Activity

MED26 or Transcription factor IIS (TFIIS) is a transcription elongation factor that increases the overall transcription rate of RNA 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.