Structures of the human Mediator and Mediator-bound preinitiation complex

Science. 2021 Jun 4;372(6546):eabg0635. doi: 10.1126/science.abg0635. Epub 2021 May 6.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • Cyclin-Dependent Kinase-Activating Kinase
  • Cyclin-Dependent Kinases / chemistry
  • Cyclin-Dependent Kinases / metabolism
  • DNA Helicases / chemistry
  • DNA-Binding Proteins / chemistry
  • Humans
  • Mediator Complex / chemistry*
  • Mediator Complex / metabolism
  • Mediator Complex Subunit 1 / chemistry
  • Models, Molecular
  • Phosphorylation
  • Promoter Regions, Genetic
  • Protein Binding
  • Protein Conformation, alpha-Helical
  • Protein Domains
  • Protein Folding
  • Protein Structure, Quaternary
  • Protein Subunits / chemistry
  • RNA Polymerase II / chemistry*
  • RNA Polymerase II / metabolism
  • Transcription Factor TFIID / chemistry*
  • Transcription Factor TFIID / metabolism
  • Transcription Factor TFIIH / chemistry
  • Transcription Factor TFIIH / metabolism
  • Transcription Initiation, Genetic*

Substances

  • DNA-Binding Proteins
  • MED1 protein, human
  • MED14 protein, human
  • MED15 protein, human
  • Med17 protein, human
  • Mediator Complex
  • Mediator Complex Subunit 1
  • Protein Subunits
  • Transcription Factor TFIID
  • XPBC-ERCC-3 protein
  • Transcription Factor TFIIH
  • Cyclin-Dependent Kinases
  • RNA Polymerase II
  • DNA Helicases
  • Cyclin-Dependent Kinase-Activating Kinase
  • CDK7 protein, human