Core Mediator structure at 3.4 Å extends model of transcription initiation complex
Core Mediator structure at 3.4 Å extends model of transcription initiation complex
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DOI：
10.1038/nature22328
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发表时间：
2017-05-11
期刊：
影响因子：
64.8
通讯作者：
Cramer, Patrick
中科院分区：
文献类型：
--
作者：
Nozawa, Kayo;Schneider, Thomas R.;Cramer, Patrick
介体是一种多蛋白共激活因子，结合转录前起始复合体(PIC)并调节RNA聚合酶(Pol)II1-3。介体头部和中间模块形成基本核心介体(CMED)(4-6)，而尾部和激酶模块起调节作用(7)。Mediator(5，8-10)的结构和它在PIC5上的位置是已知的，但原子细节仅限于Mediator亚复合体(11，12)。本文报道了裂殖酵母15亚基CMED在3.4埃分辨率下的晶体结构。结构显示了一个没有改变的头部模块(13-15)，并揭示了复杂的中间模块，我们表明这是转录所需的整体。已知的介体突变位点聚集在头部和中间模块之间的界面上，以及头部亚单位Med6的末端区域(参见16)和Med17(参考文献16)17)它系住了中间的模块。该结构导致了酿酒酵母CMED的模型，该模型可以与核心PIC(CPIC)的3.6埃冷冻电子显微镜结构(18)相结合(5)。得到的CPIC-CMED复合体的原子模型告知组成中间模块的子模块的相互作用，这些子模块称为梁、旋钮、板、连接器和挂钩。该钩通过保守的铰链(19)灵活地连接到介体，并与转录起始因子IIH(TFIIH)激酶接触，该激酶使POL II的羧基(C)-末端结构域(CTD)磷酸化，最近被定位在PIC20上。该钩还含有与CTD交联并驻留在前述摇篮(5)中的残基。这些结果为理解介体功能，包括其在TFIIH刺激CTD磷酸化中的作用提供了一个框架。
Mediator is a multiprotein co-activator that binds the transcription pre-initiation complex (PIC) and regulates RNA polymerase (Pol) II1-3. The Mediator head and middle modules form the essential core Mediator (cMed)(4-6), whereas the tail and kinase modules play regulatory roles(7). The architecture of Mediator(5,8-10) and its position on the PIC5 are known, but atomic details are limited to Mediator subcomplexes(11,12). Here we report the crystal structure of the 15-subunit cMed from Schizosaccharomyces pombe at 3.4 angstrom resolution. The structure shows an unaltered head module(13-15), and reveals the intricate middle module, which we show is globally required for transcription. Sites of known Mediator mutations cluster at the interface between the head and middle modules, and in terminal regions of the head subunits Med6 (ref. 16) and Med17 (ref. 17) that tether the middle module. The structure led to a model for Saccharomyces cerevisiae cMed that could be combined(5) with the 3.6 angstrom cryo-electron microscopy structure of the core PIC (cPIC)(18). The resulting atomic model of the cPIC-cMed complex informs on interactions of the submodules forming the middle module, called beam, knob, plank, connector, and hook. The hook is flexibly linked to Mediator by a conserved hinge(19) and contacts the transcription initiation factor IIH (TFIIH) kinase that phosphorylates the carboxy (C)-terminal domain (CTD) of Pol II and was recently positioned on the PIC20. The hook also contains residues that crosslink to the CTD and reside in a previously described cradle(5). These results provide a framework for understanding Mediator function, including its role in stimulating CTD phosphorylation by TFIIH.