![]() For the ‘top view’ shown on the right, structural disorder among Mediator subunits is indicated as semi-transparent ovals. ![]() The scaffold subunits MED17 and MED14 run through the head and middle modules and contact the tail. In this conformation (compared with the tail-extended conformation), MED23 and MED24 separate in combination with a shift in the MED16 propeller domain. We conclude with a discussion of Mediator’s potential as a therapeutic target and of future research directions.Ī | Structural features of Mediator in the tail-bent conformation 18. We propose a working model for Mediator function that combines experimental results and theoretical considerations related to enhancer–promoter interactions, which reconciles contradictory data regarding whether enhancer–promoter communication is direct or indirect. Mediator regulation of Pol II reinitiation is also discussed, in the context of transcription bursting. We further discuss how Mediator and sequence-specific DNA-binding transcription factors enable enhancer-dependent regulation of Pol II function at distal gene promoters, through the formation of molecular condensates (or transcription hubs) and chromatin loops. In this Review, we discuss Mediator structure and function, with emphasis on recent cryogenic electron microscopy data of the 4.0-MDa transcription preinitiation complex. ![]() Apart from its size, a defining feature of Mediator is its intrinsic disorder and conformational flexibility, which contributes to its ability to undergo phase separation and to interact with a myriad of regulatory factors. The Mediator complex, which in humans is 1.4 MDa in size and includes 26 subunits, controls many aspects of RNA polymerase II (Pol II) function.
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