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Nature. 2017 Apr 13;544(7649):196-201. doi: 10.1038/nature21393. Epub 2017 Mar 1.

Mediator structure and rearrangements required for holoenzyme formation.

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Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla California, USA.
Stowers Institute for Medical Research, Kansas City, Missouri, USA.
Department of Pediatrics and Institute for Genomic Medicine, University of California San Diego School of Medicine, La Jolla, California, USA.
Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City Kansas, USA.
Department of Structural Biology, Stanford University School of Medicine, Stanford, California, USA.
Department of Biochemistry &Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas, USA.


The conserved Mediator co-activator complex has an essential role in the regulation of RNA polymerase II transcription in all eukaryotes. Understanding the structure and interactions of Mediator is crucial for determining how the complex influences transcription initiation and conveys regulatory information to the basal transcription machinery. Here we present a 4.4 Å resolution cryo-electron microscopy map of Schizosaccharomyces pombe Mediator in which conserved Mediator subunits are individually resolved. The essential Med14 subunit works as a central backbone that connects the Mediator head, middle and tail modules. Comparison with a 7.8 Å resolution cryo-electron microscopy map of a Mediator-RNA polymerase II holoenzyme reveals that changes in the structure of Med14 facilitate a large-scale Mediator rearrangement that is essential for holoenzyme formation. Our study suggests that access to different conformations and crosstalk between structural elements are essential for the Mediator regulation mechanism, and could explain the capacity of the complex to integrate multiple regulatory signals.

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