A complete, 52-protein, 2.5 million dalton, Mediator-RNA polymerase II pre-initiation complex (Med-PIC) was assembled and analyzed by cryo-electron microscopy and by chemical cross-linking and mass spectrometry. The resulting complete Med-PIC structure reveals two components of functional significance, absent from previous structures, a protein kinase complex and the Mediator-activator interaction region. It thereby shows how the kinase and its target, the C-terminal domain of the polymerase, control Med-PIC interaction and transcription.
Keywords: Mediator complex; Pre-initiation complex; RNA polymerase II carboxy-terminal domain; TFIIH; TFIIK; Transcription; cross-linking; cryo-EM; mass spectrometry.
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