T4噬菌体是分子生物学和遗传学研究的模式生物，也是治疗大肠杆菌感染的潜在治疗手段。在T4噬菌体感染晚期，转录激活因子gp45结合启动子DNA并招募大肠杆菌RNA聚合酶形成转录激活复合物，从而激活晚期基因转录。由于转录激活因子gp45也是T4噬菌体DNA复制的可持续因子，因此T4噬菌体晚期基因转录激活与噬菌体DNA复制偶联。尽管已经研究了五十多年，但T4噬菌体晚期基因转录激活的分子机制仍然不够清楚，原因之一就是没有转录激活复合物的结构信息。申请人在前期转录调控研究工作的基础上，通过不断尝试，突破了体外组装转录激活复合物的瓶颈问题。申请人拟进一步解析功能状态的转录激活复合物的冷冻电镜结构，并通过生化和遗传实验验证蛋白-蛋白、蛋白-DNA相互作用，最终揭示T4噬菌体晚期基因转录激活的分子机制。本研究有助于理解转录和DNA复制偶联的分子机制，也可为更好地驾驭噬菌体提供理论依据。

As a potential treatment strategy for E. coli infection, bacteriophage T4 is a paradigm for molecular biology and genetics. At the late stage of T4 infection cycle, transcription activator gp45 binds to the promoter DNA and recruits E. coli RNA polymerase to form the transcription activation complex, which activates the transcription of late genes. Because transcription activator gp45 is a processive factor of T4 DNA replication as well, transcription activation of the late genes is coupled to its DNA replication. Although the molecular mechanism of T4 late gene transcription activation has been studied for more than 50 years, it is still elusive. One reason is that no structural information of transcription activation complex is available. Based on the previous work on transcription regulation, the applicant has bypassed the major hurdle of reconstituting the transcription activation complex in vitro through numerous trials. In the future, the applicant will solve the functional cryo-EM structure of transcription activation complex, verify the protein-protein and protein-DNA interactions in biochemical and genetic experiments, and reveal the molecular mechanism of T4 late gene transcription activation. This study will facilitate understanding of the molecular mechanism underlying transcription-replication coupling and provide a theoretical foundation to manipulate bacteriophages.