Institute for Research in Biomedicine, Barcelona Science Park, Spain.
EMBO J. 2011 Aug 9;30(18):3776-85. doi: 10.1038/emboj.2011.271.
PhoB is a two-component response regulator that activates transcription by interacting with the σ(70) subunit of the E. coli RNA polymerase in promoters in which the -35 σ(70)-recognition element is replaced by the pho box. The crystal structure of a transcription initiation subcomplex that includes the σ(4) domain of σ(70) fused with the RNA polymerase β subunit flap tip helix, the PhoB effector domain and the pho box DNA reveals how σ(4) recognizes the upstream pho box repeat. As with the -35 element, σ(4) achieves this recognition through the N-terminal portion of its DNA recognition helix, but contact with the DNA major groove is less extensive. Unexpectedly, the same recognition helix contacts the transactivation loop and helices α2 and α3 of PhoB. This result shows a simple and elegant mechanism for polymerase recruitment to pho box promoters in which the lost -35 element contacts are compensated by new ones with the activator. In addition, σ(4) is reoriented, thereby suggesting a remodelling mechanism for transcription initiation.
PhoB 是一种双组分响应调节剂，它通过与大肠杆菌 RNA 聚合酶的 σ(70)亚基相互作用，在启动子中激活转录，其中 -35 σ(70)-识别元件被 pho 盒取代。包括 σ(4)结构域与 RNA 聚合酶 β 亚基瓣状尖端螺旋、PhoB 效应结构域和 pho 盒 DNA 融合的转录起始亚复合物的晶体结构揭示了 σ(4)如何识别上游 pho 盒重复序列。与 -35 元件一样，σ(4)通过其 DNA 识别螺旋的 N 端部分实现这种识别，但与 DNA 大沟的接触不太广泛。出乎意料的是，相同的识别螺旋与转录激活环以及 PhoB 的 α2 和 α3 螺旋接触。该结果显示了一种简单而优雅的聚合酶募集机制，用于 pho 盒启动子，其中丢失的 -35 元件接触被与激活剂的新接触所补偿。此外，σ(4)被重新定向，从而提示了转录起始的重塑机制。
