FIGURE 9-39 Structure of yeast and human Mediator complexes. (a) Subunits of the S. cerevisiae and human Mediator complexes. The subunits constituting the head, middle, and tail modules of Mediator are indicated, as well as the subunits of the CDK8-kinase module (CKM) that associates with some Mediator complexes, blocking Pol II binding. (b) Cryoelectron microscopic structure of the yeast Mediator without the CKM. (Left) The head, middle, and tail modules composed of the subunits listed above are color-coded. (Right) The structure of a complex of Mediator with Pol II, called the holoenzyme, suggests that the Mediator modules rotate relative to one another as shown to create a surface that binds Pol II.

[Part (b) republished with permission of Elsevier, from Tsai, K.L., “Subunit architecture and functional modular rearrangements of the transcriptional mediator complex,” Cell, 2014, 157(6): 1430–1444; permission conveyed through Copyright Clearance Center, Inc.]