TY - JOUR TI - Crl activates transcription by stabilizing active conformation of the master stress transcription initiation factor AU - Xu, Juncao AU - Cui, Kaijie AU - Shen, Liqiang AU - Shi, Jing AU - Li, Lingting AU - You, Linlin AU - Fang, Chengli AU - Zhao, Guoping AU - Feng, Yu AU - Yang, Bei AU - Zhang, Yu A2 - Murakami, Katsuhiko A2 - Storz, Gisela A2 - Murakami, Katsuhiko VL - 8 PY - 2019 DA - 2019/12/17 SP - e50928 C1 - eLife 2019;8:e50928 DO - 10.7554/eLife.50928 UR - https://doi.org/10.7554/eLife.50928 AB - σS is a master transcription initiation factor that protects bacterial cells from various harmful environmental stresses including antibiotic pressure. Although its mechanism remains unclear, it is known that full activation of σS-mediated transcription requires a σS-specific activator, Crl. In this study, we determined a 3.80 Å cryo-EM structure of an Escherichia coli transcription activation complex (E. coli Crl-TAC) comprising E. coli σS-RNA polymerase (σS-RNAP) holoenzyme, Crl, and a nucleic-acid scaffold. The structure reveals that Crl interacts with domain 2 of σS (σS2) and the RNAP core enzyme, but does not contact promoter DNA. Results from subsequent hydrogen-deuterium exchange mass spectrometry (HDX-MS) indicate that Crl stabilizes key structural motifs within σS2 to promote the assembly of the σS-RNAP holoenzyme and also to facilitate formation of an RNA polymerase–promoter DNA open complex (RPo). Our study demonstrates a unique DNA contact-independent mechanism of transcription activation, thereby defining a previously unrecognized mode of transcription activation in cells. KW - transcription factors KW - RNA polymerase KW - Crl KW - transcription activation KW - sigma factor KW - stress response JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -