Fig. 6. σ⁷⁰ NCR adopts a different conformation and interacts with β' clamp during promoter escape.

a Superimposition of RD_e1 with EcmrR-RP_itc-4nt structures illustrates the large conformational changes of σ⁷⁰ NCR and σ₂ domain. The EcmrR NTD that is proximal to σ⁷⁰ NCR is colored in yellow. b A close-up view of the σ⁷⁰ NCR and β' clamp-toe interface superimposed with the cryo-EM density (blue surface) contoured at 5.5 σ. c Electrostatic surfaces of σ⁷⁰ NCR and β' clamp-toe. The unit of electrostatic potential is kT/e⁻. d Interactions between σ⁷⁰ NCR and β' clamp-toe. Hydrogen bonds and salt bridges are shown as gray dotted lines. e Superimposition of σ⁷⁰ NCR (bright colors) together with σ₂ domain (pale colors) in RD_e1 with those in EcmrR-RP_itc-4nt, showing that σ₂ domain stays largely static relative to σ⁷⁰ NCR in the two structures. f Comparison of the σ₂-β' clamp coiled-coil interactions between the structures of EcmrR-RP_itc-4nt and RD_e1. Hydrogen bonds and salt bridges are shown as yellow dotted lines. The surface areas buried between β' clamp coiled-coil and σ₂ in the two structures are indicated.