TY - JOUR TI - Structural basis of transcription inhibition by the DNA mimic protein Ocr of bacteriophage T7 AU - Ye, Fuzhou AU - Kotta-Loizou, Ioly AU - Jovanovic, Milija AU - Liu, Xiaojiao AU - Dryden, David TF AU - Buck, Martin AU - Zhang, Xiaodong A2 - Darst, Seth A2 - Wolberger, Cynthia VL - 9 PY - 2020 DA - 2020/02/10 SP - e52125 C1 - eLife 2020;9:e52125 DO - 10.7554/eLife.52125 UR - https://doi.org/10.7554/eLife.52125 AB - Bacteriophage T7 infects Escherichia coli and evades the host restriction/modification system. The Ocr protein of T7 was shown to exist as a dimer mimicking DNA and to bind to host restriction enzymes, thus preventing the degradation of the viral genome by the host. Here we report that Ocr can also inhibit host transcription by directly binding to bacterial RNA polymerase (RNAP) and competing with the recruitment of RNAP by sigma factors. Using cryo electron microscopy, we determined the structures of Ocr bound to RNAP. The structures show that an Ocr dimer binds to RNAP in the cleft, where key regions of sigma bind and where DNA resides during transcription synthesis, thus providing a structural basis for the transcription inhibition. Our results reveal the versatility of Ocr in interfering with host systems and suggest possible strategies that could be exploited in adopting DNA mimicry as a basis for forming novel antibiotics. KW - Ocr KW - bacteriophage KW - transcription KW - DNA mimicry proteins KW - RNAP KW - cryo EM JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -