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Mediator itself is a large complex consisting of approximately 22 polypeptides. This large structure is formed from 3 domains: the head, middle and tail which as unit can either exist on its own or associated with RNA polymerase II via the c-terminal domain.


The main function of the mediator complex is to interact with upstream activators on the mRNA, as well as with RNA Polymerase II to initiate transcription. Activators cannot activate transcription independently In vitro, and so the mediator complex is believed to aid the initiation of transcription via interactions with activators at certain locations on the mediator complex. These mediator-activator interactions, along with other transcription factors, aid the recruitment and assembly of the pre-initiation complex (PIC)[1]

Discovery of Mediator

Mediator was first wrote about in a 1990 paper by Kelleher, Flanagan and Kornberg titled 'A novel mediator between activator proteins and the RNA polymerase II transcription apparatus'[2]. They found a gene activator protein in yeast which aided In vitro transcription of the genetic material. This research led to a Nobel Prize in Chemistry for Kornberg in 2006[3].


  1. Poss Z., Ebmeier C., Taatjes D. (2013) Critical Views in Biochemistry and Molecular Biology, Volume 38, Page 575-608.
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