美国国立卫生研究院癌症研究中心Rafael Casellas和科罗拉多大学 Francisco J. Asturias小组近日取得一项新成果。他们提出可塑转录中介体复合物可以作为启动子和增强子之间功能性而非结构性的桥梁。该研究于2019年8月22日发表于国际学术期刊《细胞》。
该研究结合CRISPR-Cas9遗传筛选、degron测定、Hi-C和冷冻电镜（cryo-EM）的方法解析了哺乳动物中介体（mMED）的功能和结构。研究人员利用B细胞、T细胞以及胚胎干细胞（ESC）中的中介体缺失分析，确定了负责Pol II在全基因组招募所需的核心亚基。相反，中介体非必需亚基的丧失主要影响启动子与多种增强子的结合。然而，与目前已知的模型相反，mMED和Pol II对调节双链束缚的DNA是非必须的，这种调节需要结构蛋白的拓扑改变。 Cryo-EM分析发现中介体有一个保守的核心，非必需亚基增加了其尾部模块结构的复杂性，尾部模块是主要的转录因子识别靶点。尾部结构的改变显着增加Pol II和激酶模块的相互作用。研究人员提出Mediator结构的可塑性使其能够整合和传递调控信号，并在启动子和增强者之间充当功能性而非结构性桥梁。
据介绍，中介体在真核转录中起关键作用，但对其作用机制知之甚少。
附：英文原文
Title: A Pliable Mediator Acts as a Functional Rather Than an Architectural Bridge between Promoters and Enhancers
Author:Laila El Khattabi,Haiyan Zhao,Jens Kalchschmidt,Natalie Young,Seolkyoung Jung,Peter Van Blerkom,Philippe Kieffer-Kwon,Kyong-Rim Kieffer-Kwon,Solji Park,Xiang Wang,Jordan Krebs,Subhash Tripathi,Noboru Sakabe,Débora R. Sobreira,Su-Chen Huang,Suhas S.P. Rao,Nathanael Pruett,Daniel Chauss,Erica Sadler,Andrea Lopez,Marcelo A. Nóbrega,Erez Lieberman Aiden,Francisco J. Asturias,Rafael Casellas
Issue&Volume: Volume 178 Issue 5
Abstract: While Mediator plays a key role in eukaryotic transcription, little is known about its mechanism of action. This study combines CRISPR-Cas9 genetic screens, degron assays, Hi-C, and cryoelectron microscopy (cryo-EM) to dissect the function and structure of mammalian Mediator (mMED). Deletion analyses in B, T, and embryonic stem cells (ESC) identified a core of essential subunits required for Pol II recruitment genome-wide. Conversely, loss of non-essential subunits mostly affects promoters linked to multiple enhancers. Contrary to current models, however, mMED and Pol II are dispensable to physically tether regulatory DNA, a topological activity requiring architectural proteins. Cryo-EM analysis revealed a conserved core, with non-essential subunits increasing structural complexity of the tail module, a primary transcription factor target. Changes in tail structure markedly increase Pol II and kinase module interactions. We propose that Mediator’s structural pliability enables it to integrate and transmit regulatory signals and act as a functional, rather than an architectural bridge, between promoters and enhancers.
DOI: https://doi.org/10.1016/j.cell.2019.07.011
Source: https://www.cell.com/cell/fulltext/S0092-8674(19)30776-7