RNA polymerase (RNAP) is a major target of gene regulation. Thermus thermophilus bacteriophage P23–45 encodes two RNAP binding proteins, gp39 and gp76, which shut off host gene transcription while allowing orderly transcription of phage genes. We previously reported the structure of the T. thermophilus RNAP•σ^A holoenzyme complexed with gp39. Here, we solved the structure of the RNAP•σ^A holoenzyme bound with both gp39 and gp76, which revealed an unprecedented inhibition mechanism by gp76. The acidic protein gp76 binds within the RNAP cleft and occupies the path of the template DNA strand at positions –11 to –4, relative to the transcription start site at +1. Thus, gp76 obstructs the formation of an open promoter complex and prevents transcription by T. thermophilus RNAP from most host promoters. gp76 is less inhibitory for phage transcription, as tighter RNAP interaction with the phage promoters allows the template DNA to compete with gp76 for the common binding site. gp76 also inhibits Escherichia coli RNAP highlighting the template–DNA binding site as a new target site for developing antibacterial agents.

中文翻译：

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甲栖热通过防止开放启动子复合体的形成过程中的模板DNA链加载噬菌体蛋白抑制宿主RNA聚合酶

RNA聚合酶（RNAP）是基因调控的主要目标。嗜热栖热菌噬菌体P23–45编码两个RNAP结合蛋白gp39和gp76，它们关闭宿主基因转录，同时允许噬菌体基因有序转录。我们之前曾报道过嗜热链球菌RNAP•σ与gp39复合^的全酶的结构。在这里，我们解决了RNAP•σ的结构^一全酶与gp39和gp76都结合，这揭示了gp76前所未有的抑制机制。酸性蛋白gp76结合在RNA裂隙中，并占据模板DNA链相对于转录起始位点+1的位置–11至–4的路径。因此，gp76阻碍了开放启动子复合物的形成，并阻止嗜热链球菌RNAP从大多数宿主启动子转录。gp76对噬菌体转录的抑制作用较小，因为与噬菌体启动子的更紧密的RNAP相互作用使模板DNA与gp76竞争共同的结合位点。gp76还抑制大肠杆菌RNAP，突出了模板DNA结合位点作为开发抗菌剂的新目标位点。