Chen Xizi, Yin Xiaotong, Li Jiabei, Wu Zihan, Qi Yilun, Wang Xinxin, Liu Weida, Xu Yanhui
Fudan University Shanghai Cancer Center, Institutes of Biomedical Sciences, State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Radiation Oncology, and Shanghai Key Laboratory of Medical Epigenetics, Shanghai Medical College of Fudan University, Shanghai 200032, China.
International Co-laboratory of Medical Epigenetics and Metabolism, Ministry of Science and Technology, China, Department of Systems Biology for Medicine, School of Basic Medical Sciences, Shanghai Medical College of Fudan University, Shanghai 200032, China.
Science. 2021 Jun 4;372(6546). doi: 10.1126/science.abg0635. Epub 2021 May 6.
The 1.3-megadalton transcription factor IID (TFIID) is required for preinitiation complex (PIC) assembly and RNA polymerase II (Pol II)-mediated transcription initiation on almost all genes. The 26-subunit Mediator stimulates transcription and cyclin-dependent kinase 7 (CDK7)-mediated phosphorylation of the Pol II C-terminal domain (CTD). We determined the structures of human Mediator in the Tail module-extended (at near-atomic resolution) and Tail-bent conformations and structures of TFIID-based PIC-Mediator (76 polypeptides, ~4.1 megadaltons) in four distinct conformations. PIC-Mediator assembly induces concerted reorganization (Head-tilting and Middle-down) of Mediator and creates a Head-Middle sandwich, which stabilizes two CTD segments and brings CTD to CDK7 for phosphorylation; this suggests a CTD-gating mechanism favorable for phosphorylation. The TFIID-based PIC architecture modulates Mediator organization and TFIIH stabilization, underscoring the importance of TFIID in orchestrating PIC-Mediator assembly.
130万道尔顿的转录因子IID（TFIID）是几乎所有基因上起始前复合物（PIC）组装和RNA聚合酶II（Pol II）介导的转录起始所必需的。由26个亚基组成的中介体刺激转录以及细胞周期蛋白依赖性激酶7（CDK7）介导的Pol II C末端结构域（CTD）的磷酸化。我们确定了处于尾部模块延伸构象（接近原子分辨率）和尾部弯曲构象的人类中介体的结构，以及基于TFIID的PIC-中介体（76种多肽，约410万道尔顿）在四种不同构象下的结构。PIC-中介体组装诱导中介体的协同重组（头部倾斜和中部下移），并形成头部-中部夹层结构，该结构稳定了两个CTD片段，并将CTD带到CDK7处进行磷酸化；这表明存在一种有利于磷酸化的CTD门控机制。基于TFIID的PIC结构调节中介体的组织和TFIIH的稳定性，强调了TFIID在协调PIC-中介体组装中的重要性。
