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. 2021 Jan 1;17(1):328–338. doi: 10.7150/ijbs.52290

Figure 1.

Figure 1

The main structure and function of the mediator complex (MED). The MED is composed of four parts: the head, middle, tail, and CKM. The CKM includes CDK8/19, Cyc C/CCNC, MED12/12L, and MED13/13L. (A) The CKM associates with the MED via interaction between MED13 and a “hook” at the end of the MED (middle module). Targeted degradation of MED13 can affect the association between the CKM and the MED. (B) An activator (Act) recruits the MED to an enhancer and then recruits GTFs. (C) The MED helps to recruit RNA polymerase (Pol) II to the promoter via interaction with the non-phosphorylated carboxy-terminal domain (CTD) of RNA polymerase II. MED also helps recruit other factors to promote the formation of the preinitiation complex. (D) This process includes CKM dissociation from the MED. (E) Then, the CTD of RNA polymerase II is phosphorylated (P-CTD) by the GTF TFIIH, which is accompanied by MED dissociation, thereby allowing RNA polymerase II to escape from the promoter and initiate transcription. The MED also regulates RNA polymerase II pausing and elongation. (CKM, cyclin-dependent kinase 8 (CDK8) kinase module; GTF, general transcription factor).