TY - JOUR T1 - Crl activates transcription by stabilizing the active conformation of the master stress factor σ<sup>S</sup> JF - bioRxiv DO - 10.1101/721944 SP - 721944 AU - Juncao Xu AU - Kaijie Cui AU - Liqiang Shen AU - Jing Shi AU - Lingting Li AU - Linlin You AU - Chengli Fang AU - Guoping Zhao AU - Yu Feng AU - Bei Yang AU - Yu Zhang Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/08/01/721944.abstract N2 - σS is a master transcription initiation factor that protects bacterial cells from various harmful environmental stresses and 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 E. coli transcription activation complex (E. coli Crl-TAC) comprising E. coli σS-RNAP holoenzyme, Crl, and a nucleic-acid scaffold. The structure reveals that Crl interacts with the domain 2 of σS (σS2), sharing no interaction with promoter DNA. Subsequent hydrogen-deuterium exchange mass spectrometry (HDX-MS) results indicate that Crl stabilizes key structural motifs of σS2 to promote the assembly of σS-RNAP holoenzyme and also to facilitate formation of the 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. ER -