σ⁷⁰-dependent Transcription Pausing in Escherichia coli

After promoter escape in Escherichia coli, the initiating σ⁷⁰ factor is retained by core RNA polymerase (RNAP) for at least tens of nucleotides. While it is bound, σ⁷⁰ can engage a repeat of a promoter DNA element located downstream of the promoter and thereby induce a transcription pause. The σ⁷⁰-dependent promoter-proximal pause that occurs at all lambdoid phage late gene promoters is essential to regulation of the late gene operons. Several, and possibly many, E. coli promoters have associated σ⁷⁰-dependent pauses. Clearly characterized σ⁷⁰-dependent pauses occur within 25 nucleotides of the start site, but σ⁷⁰-dependent pausing might occur farther downstream as well. In this review, we summarize evidence for σ⁷⁰-dependent promoter-proximal and promoter-distal pausing, and we discuss its potential regulatory function and mechanistic basis.