Abstract
The 1.3-megadalton transcription factor IID (TFIID) is required for preinitiation complex (PIC) assembly and RNA polymerase II (Pol II)-mediated transcription initiation on almost all genes. The 26-subunit Mediator stimulates transcription and cyclin-dependent kinase 7 (CDK7)-mediated phosphorylation of the Pol II C-terminal domain (CTD). We determined the structures of human Mediator in the Tail module-extended (at near-atomic resolution) and Tail-bent conformations and structures of TFIID-based PIC-Mediator (76 polypeptides, ~4.1 megadaltons) in four distinct conformations. PIC-Mediator assembly induces concerted reorganization (Head-tilting and Middle-down) of Mediator and creates a Head-Middle sandwich, which stabilizes two CTD segments and brings CTD to CDK7 for phosphorylation; this suggests a CTD-gating mechanism favorable for phosphorylation. The TFIID-based PIC architecture modulates Mediator organization and TFIIH stabilization, underscoring the importance of TFIID in orchestrating PIC-Mediator assembly.
Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Cryoelectron Microscopy
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Cyclin-Dependent Kinase-Activating Kinase
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Cyclin-Dependent Kinases / chemistry
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Cyclin-Dependent Kinases / metabolism
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DNA Helicases / chemistry
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DNA-Binding Proteins / chemistry
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Humans
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Mediator Complex / chemistry*
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Mediator Complex / metabolism
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Mediator Complex Subunit 1 / chemistry
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Models, Molecular
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Phosphorylation
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Promoter Regions, Genetic
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Protein Binding
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Protein Conformation, alpha-Helical
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Protein Domains
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Protein Folding
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Protein Structure, Quaternary
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Protein Subunits / chemistry
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RNA Polymerase II / chemistry*
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RNA Polymerase II / metabolism
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Transcription Factor TFIID / chemistry*
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Transcription Factor TFIID / metabolism
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Transcription Factor TFIIH / chemistry
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Transcription Factor TFIIH / metabolism
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Transcription Initiation, Genetic*
Substances
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DNA-Binding Proteins
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MED1 protein, human
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MED14 protein, human
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MED15 protein, human
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Med17 protein, human
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Mediator Complex
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Mediator Complex Subunit 1
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Protein Subunits
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Transcription Factor TFIID
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XPBC-ERCC-3 protein
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Transcription Factor TFIIH
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Cyclin-Dependent Kinases
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RNA Polymerase II
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DNA Helicases
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Cyclin-Dependent Kinase-Activating Kinase
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CDK7 protein, human