Shi Jing, Wen Aijia, Jin Sha, Gao Bo, Huang Yang, Feng Yu
Department of Biophysics, and Department of Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China.
Department of Microbiology and Immunology, School of Medicine & Holistic Integrative Medicine, Nanjing University of Chinese Medicine, Nanjing, China.
Nat Commun. 2021 Feb 18;12(1):1131. doi: 10.1038/s41467-021-21392-0.
Transcription activation of bacteriophage T4 late genes is accomplished by a transcription activation complex containing RNA polymerase (RNAP), the promoter specificity factor gp55, the coactivator gp33, and a universal component of cellular DNA replication, the sliding clamp gp45. Although genetic and biochemical studies have elucidated many aspects of T4 late gene transcription, no precise structure of the transcription machinery in the process is available. Here, we report the cryo-EM structures of a gp55-dependent RNAP-promoter open complex and an intact gp45-dependent transcription activation complex. The structures reveal the interactions between gp55 and the promoter DNA that mediate the recognition of T4 late promoters. In addition to the σR2 homology domain, gp55 has a helix-loop-helix motif that chaperons the template-strand single-stranded DNA of the transcription bubble. Gp33 contacts both RNAP and the upstream double-stranded DNA. Gp45 encircles the DNA and tethers RNAP to it, supporting the idea that gp45 switches the promoter search from three-dimensional diffusion mode to one-dimensional scanning mode.
噬菌体T4晚期基因的转录激活是由一个转录激活复合物完成的，该复合物包含RNA聚合酶（RNAP）、启动子特异性因子gp55、共激活因子gp33以及细胞DNA复制的一个通用成分——滑动夹gp45。尽管遗传和生化研究已经阐明了T4晚期基因转录的许多方面，但在此过程中转录机制的精确结构尚无可用信息。在这里，我们报告了gp55依赖性RNAP-启动子开放复合物和完整的gp45依赖性转录激活复合物的冷冻电镜结构。这些结构揭示了gp55与启动子DNA之间的相互作用，这些相互作用介导了对T4晚期启动子的识别。除了σR2同源结构域外，gp55还有一个螺旋-环-螺旋基序，它陪伴转录泡的模板链单链DNA。Gp33与RNAP和上游双链DNA都有接触。Gp45环绕DNA并将RNAP拴在其上，支持了gp45将启动子搜索从三维扩散模式转换为一维扫描模式的观点。
