PMID: 30858373
Li L, Fang C, Zhuang N, Wang T, Zhang Y
Structural basis for transcription initiation by bacterial ECF sigma factors.
Nat Commun. 2019 Mar 11;10(1):1153. doi: 10.1038/s41467-019-09096-y.
Bacterial RNA polymerase employs extra-cytoplasmic function (ECF) sigma factors to regulate context-specific gene expression programs. Despite being the most abundant and divergent sigma factor class, the structural basis of ECF sigma factor-mediated transcription initiation remains unknown. Here, we determine a crystal structure of Mycobacterium tuberculosis (Mtb) RNAP holoenzyme comprising an RNAP core enzyme and the ECF sigma factor sigma(H) (sigma(H)-RNAP) at 2.7 A, and solve another crystal structure of a transcription initiation complex of Mtb sigma(H)-RNAP (sigma(H)-RPo) comprising promoter DNA and an RNA primer at 2.8 A. The two structures together reveal the interactions between sigma(H) and RNAP that are essential for sigma(H)-RNAP holoenzyme assembly as well as the interactions between sigma(H)-RNAP and promoter DNA responsible for stringent promoter recognition and for promoter unwinding. Our study establishes that ECF sigma factors and primary sigma factors employ distinct mechanisms for promoter recognition and for promoter unwinding.