Larivière Laurent, Geiger Sebastian, Hoeppner Sabine, Röther Susanne, Strässer Katja, Cramer Patrick
Gene Center Munich, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
Nat Struct Mol Biol. 2006 Oct;13(10):895-901. doi: 10.1038/nsmb1143. Epub 2006 Sep 10.
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.
中介体头部模块刺激基础RNA聚合酶II（Pol II）转录并实现转录调控。我们在此表明，头部亚基Med8、Med18和Med20形成一个具有两个子模块的亚复合物（Med8/18/20）。Med8高度保守的N端结构域形成一个子模块，该子模块在体外结合TATA盒结合蛋白（TBP），且在体内至关重要。第二个子模块由Med8的C端区域（Med8C）、Med18和Med20组成。对该子模块的X射线分析表明，Med18和Med20形成相关的β桶状折叠。Med8C/18/20子模块上一个保守的假定蛋白质相互作用面包括因srb突变而改变的位点，这些突变可抵消Pol II截短导致的缺陷。我们的结果和已发表的数据支持Med8/18/20亚复合物在起始复合物形成中的积极作用，并表明中介体头部包含一个可被转录激活因子调节的多部分TBP结合位点。
