Fig. 1.

Architecture of σ⁷⁰-dependent paused TECs. As the TEC reaches +13, σ⁷⁰-dependent pausing is induced through contacts between the nontemplate strand −10-like and discriminator sequences by σ⁷⁰ regions 2 and 1.2, respectively. The +16 paused, scrunched complex is formed when the −10-like sequence-bound TEC continues to synthesize RNA by DNA scrunching. The TEC encounters an EPS at +16 and can enter into a stable, paused state. Upon synthesis to +17, if RNAP fails to break the σ⁷⁰:DNA interaction, the TEC backtracks into an arrested state in which σ⁷⁰ remains bound to the −10-like sequence and the RNA 3′-OH is displaced downstream from the active center.