title: Structure and TBP binding of the Mediator head subcomplex Med8-Med18-Med20.
abstract: 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.
authors.affiliation: Gene Center Munich, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
authors.forename: Laurent
authors.initials: L
authors.lastname: Larivière
authors.forename: Sebastian
authors.initials: S
authors.lastname: Geiger
authors.forename: Sabine
authors.initials: S
authors.lastname: Hoeppner
authors.forename: Susanne
authors.initials: S
authors.lastname: Röther
authors.forename: Katja
authors.initials: K
authors.lastname: Strässer
authors.forename: Patrick
authors.initials: P
authors.lastname: Cramer
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019281:Dimerization; D056892:Mediator Complex; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D035181:TATA-Box Binding Protein / Q000737:chemistry* / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C421882:MED8 protein, S cerevisiae; D056892:Mediator Complex; D029701:Saccharomyces cerevisiae Proteins; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; D012319:RNA Polymerase II