Mediator (coactivator)

Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes. It was discovered by Roger D. Kornberg, winner of the 2006 Nobel Prize in Chemistry. It is also referred to in scientific literature as the vitamin D receptor interacting protein (DRIP) coactivator complex and the thyroid hormone receptor-associated proteins (TRAP).

The mediator complex is required for the successful transcription of nearly all class II gene promoters in yeast. It works in the same manner in mammals. The human Mediator complex has 31+ subunits and is 1.2 MDa in size. Its large surface area provides great potential for protein–protein interaction, even though its sequences do not contain many predicted functional domains. Mediator has been shown to associate with general transcription factors, as well as RNA polymerase II, and is essential for activator-dependent transcription. It has also been demonstrated that the Mediator complex is involved in activator-independent transcription, implying that it may provide a fundamental control of the formation of the initiation complex. Mediator functions as a coactivator and binds to the C-terminal domain of RNA polymerase II holoenzyme, acting as a bridge between this enzyme and transcription factors.