Mediator Structure and Interaction with the Basal Transcription Machinery

Abstract

Understanding the structure and conformational dynamics of Mediator is critical for unraveling the essential role the complex plays in regulation of eukaryotic transcription initiation. We used single particle macromolecular electron microscopy (EM) to study the conformational variability of Mediator and that information enabled us to determine a cryo‐EM structure of the complex at ~26Å resolution. Comparing the structures of free and RNA polymerase II (RNAPII)‐associated Mediator made possible a detailed description of Mediator structural modules and the rearrangement they undergo upon interaction with RNAPII, both of which appear to be conserved from yeast to humans. We have also pursued independent EM analysis of the Head module responsible for control of the Mediator‐RNAPII interaction. Conformational analysis of a recombinant Head module revealed distinct conformations and comparison with the structures of sub‐complexes provided information about subunit organization. All of this information, along with results from biochemical and structural analysis of the interaction of the Head module with the TATA‐binding protein (TBP) and RNAPII subunits Rpb4 and Rpb7, suggest a possible mechanism for Mediator regulation of RNAPII interaction with promoter DNA.Supporteb by NIH R01 GM67167