School of Life Sciences, University of Science and Technology of China, Hefei, 230026, China.
Protein Cell. 2013 Dec;4(12):911-20. doi: 10.1007/s13238-013-3069-y. Epub 2013 Sep 16.
Mediator is a highly conserved large protein complex (25 proteins, >1000 kDa) and preeminently responsible for eukaryotic transcription, which contains a dissociable 'Cdk8 module'. Although increasing evidence demonstrates that Cdk8 module plays both positive and negative roles in transcription regulation, the detailed structure, and subunit organization, molecular mechanism how it regulates transcription remain elusive. Here we used single-particle electron microscopy to characterize the structure and subunit organization of the Cdk8 module and illuminated the substantial mobility of the Med13 subunit results in the structural flexibility. The Cdk8 module interaction with core Mediator is concurrent with active transcription in vivo. An interaction with the Cdk8 module induces core Mediator into very extended conformation in vitro, which is presumed to be an active functional state of Mediator. Taken together, our results illuminated the detailed architecture of Cdk8 module, and suggested the Cdk8 module could positively regulate transcription by modulating Mediator conformation.
中介体是一种高度保守的大型蛋白复合物（25 种蛋白，>1000 kDa），主要负责真核转录，其中包含一个可分离的“CDK8 模块”。尽管越来越多的证据表明 CDK8 模块在转录调控中发挥着正反两方面的作用，但它调节转录的详细结构和亚基组织、分子机制仍不清楚。在这里，我们使用单颗粒电子显微镜来描绘 CDK8 模块的结构和亚基组织，并阐明 Med13 亚基的大量移动导致结构的灵活性。CDK8 模块与核心中介体的相互作用与体内的活跃转录同时发生。与 CDK8 模块的相互作用将核心中介体诱导成非常伸展的构象，体外，这被认为是中介体的一种活跃的功能状态。总之，我们的结果阐明了 CDK8 模块的详细结构，并表明 CDK8 模块可以通过调节中介体构象来正向调节转录。
