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Nat Struct Mol Biol. 2006 Oct;13(10):895-901. Epub 2006 Sep 10.

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

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1
Gene Center Munich, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany.

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.

PMID:
16964259
DOI:
10.1038/nsmb1143
[Indexed for MEDLINE]
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