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Structure and TBP binding of the Mediator head subcomplex Med8-Med18-Med20.

The Mediator head module stimulates basal RNA polymerase II (Pol II) transcription and enables transcriptional regulation. Here we show that the head subunits Med8, Med18 and Med20 form a subcomplex (Med8/18/20) with two submodules. The highly conserved N-terminal domain of Med8 forms one submodule that binds the TATA box-binding protein (TBP) in vitro and is essential in vivo. The second submodule consists of the C-terminal region of Med8 (Med8C), Med18 and Med20. X-ray analysis of this submodule reveals that Med18 and Med20 form related beta-barrel folds. A conserved putative protein-interaction face on the Med8C/18/20 submodule includes sites altered by srb mutations, which counteract defects resulting from Pol II truncation. Our results and published data support a positive role of the Med8/18/20 subcomplex in initiation-complex formation and suggest that the Mediator head contains a multipartite TBP-binding site that can be modulated by transcriptional activators.

Pubmed ID: 16964259


  • Larivière L
  • Geiger S
  • Hoeppner S
  • Röther S
  • Strässer K
  • Cramer P


Nature structural & molecular biology

Publication Data

October 5, 2006

Associated Grants


Mesh Terms

  • Amino Acid Sequence
  • Binding Sites
  • Dimerization
  • Mediator Complex
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Folding
  • Protein Structure, Tertiary
  • RNA Polymerase II
  • Saccharomyces cerevisiae Proteins
  • Sequence Homology, Amino Acid
  • Structure-Activity Relationship
  • TATA-Box Binding Protein
  • Transcription Factors
  • Transcription, Genetic