小柯机器人

德国马克斯·普朗克生物物理化学研究所Patrick Cramer研究团队解析出人类中介体–RNA聚合酶II起始前复合物的结构。这一研究成果于2021年4月27日在线发表在国际学术期刊《自然》上。

据研究人员介绍，中介体是一种保守的共激活因子，可在真核基因中实现受调控的转录起始。中介体由转录激活因子招募，并结合起始前复合物（PIC）来引起RNA聚合酶II（Pol II）磷酸化和启动子解脱。

研究人员获得了重组的人类中介体，并重组了50个亚基的中介体-PIC复合物，并通过冷冻电镜确定了复合物的结构。中介体使用其头模块来接触Pol II茎和通用转录因子TFIIB和TFIIE，类似于相应酵母复合物中的中介体-PIC相互作用。多细胞生物的亚基MED27-MED30与MED14和MED17中的暴露区域相关联，进而形成与激活因子结合的中介体尾巴模块的近端部分。

中介体将通用转录因子TFIIH的柔性连接的CDK激活激酶（CAK）定位在Pol II的C末端重复域（CTD）的接头附近。中介体肩部结构域拥有CAK亚基CDK7，而钩状结构域则与位于激酶活性位点两侧的CDK7元件相接触。肩和钩分别位于中介体的头部模块和中间模块中，它们可以彼此相对移动，并且可以诱导CDK7激酶的活性构象来变构刺激CTD磷酸化。

附：英文原文

Title: Structure of human Mediator–RNA polymerase II pre-initiation complex

Author: Srinivasan Rengachari, Sandra Schilbach, Shintaro Aibara, Christian Dienemann, Patrick Cramer

Issue&Volume: 2021-04-26

Abstract: Mediator is a conserved coactivator that enables regulated transcription initiation at eukaryotic genes1–3. Mediator is recruited by transcriptional activators and binds the pre-initiation complex (PIC) to stimulate RNA polymerase II (Pol II) phosphorylation and promoter escape1–6. Here we prepare a recombinant human Mediator, reconstitute a 50-subunit Mediator-PIC complex, and determine the structure of the complex by cryo-EM. Mediator uses its head module to contact the Pol II stalk and the general transcription factors TFIIB and TFIIE, resembling the Mediator-PIC interactions in the corresponding yeast complex7–9. The metazoan subunits MED27-MED30 associate with exposed regions in MED14 and MED17 to form the proximal part of the Mediator tail module that binds activators. Mediator positions the flexibly linked CDK-activating kinase (CAK) of the general transcription factor TFIIH near the linker to the C-terminal repeat domain (CTD) of Pol II. The Mediator shoulder domain holds the CAK subunit CDK7, whereas the hook domain contacts a CDK7 element that flanks the kinase active site. The shoulder and hook reside in the Mediator head and middle modules, respectively, which can move relative to each other and may induce an active conformation of the CDK7 kinase to allosterically stimulate CTD phosphorylation.

DOI: 10.1038/s41586-021-03555-7

Source: https://www.nature.com/articles/s41586-021-03555-7

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