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.