RNAP holoenzyme and the interaction of RNAP with σ70-dependent promoters. Structure-based cartoons (left to right) depict RNAP holoenzyme, RPc (closed complex), RPo (open complex), and EC (elongating complex) with σ70 in yellow, core (β,β',α2, and ω) in turquoise, DNA in magenta, and RNA in purple. In holoenzyme, the positions of σ70 Regions 1.1, 2, 3, and 4, the α-CTDs, the β-flap, and the β,β' jaws are identified. In RPc, contact can be made between RNAP and promoter dsDNA elements: two UP elements with each of the α-CTDs, the -35 element with σ70 Region 4, TGn (positions -15 to -13) with σ70 Region 3, and positions -12/-11 of the -10 element with σ70 Region 2. σ70 Region 1.1 lies in the downstream DNA channel formed by portions of β and β' and the β',β' jaws are open. In RPo, unwinding of the DNA and conformational changes within RNAP result in a sharp bend of the DNA into the active site with the formation of the transcription bubble surrounding the start of transcription, the interaction of σ70 Region 2 with nontemplate ssDNA in the -10 element, movement of Region 1.1 from the downstream DNA channel, and contact between the downstream DNA and the β' clamp. In EC, σ70 and the promoter DNA have been released. The newly synthesized RNA remains annealed to the DNA template in the RNA/DNA hybrid as the previously synthesized RNA is extruded through the RNA exit channel past the β-flap.