Sunday, 10 September, 2006
Structure and TBP binding of the Mediator head subcomplex Med8-Med18-Med20
L. Lariviere, S. Geiger, S. Hoeppner, S. Röther, K. Sträßer & P.Cramer -
Nature Struct. Mol. Biol. 13, 895 (2006)
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) invitro 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 ininitiation-complex formation and suggest that the Mediator head contains a multipartite TBP-binding site that can be modulated by transcriptional activators.