the transcription machinery including RNA polymerase (RNAP). In Escherichia coli, a
primary σ 70 factor forms the RNAP holoenzyme to express housekeeping genes. The σ 70
contains a large insertion between the conserved regions 1.2 and 2.1, the σ non-conserved
region (σ NCR), but its function remains to be elucidated. In this study, we determined the
cryo-EM structures of the E. coli RNAP σ 70 holoenzyme and its complex with promoter DNA …