The σ⁷⁰ subunit of RNA polymerase mediates a promoter-proximal pause at the lac promoter

The σ⁷⁰ subunit of RNA polymerase plays an essential role in transcription initiation. In addition, σ⁷⁰ has a critical regulatory role during transcription elongation at the bacteriophage λ late promoter, σP^R′. At this promoter, σ ⁷⁰ mediates a pause in early elongation through contact with a DNA sequence element in the initially transcribed region that resembles a promoter -10 element. Here we provide evidence that σ⁷⁰ also mediates a pause in early elongation at the lac promoter (plac). Like that at λP_R′, the pause at plac is facilitated by a sequence element in the initially transcribed region that resembles a promoter -10 element. Using biophysical analysis, we demonstrate that the pause-inducing sequence element at plac stabilizes the interaction between σ ⁷⁰ and the remainder of the transcription elongation complex. Bioinformatic analysis suggests that promoter-proximal σ ⁷⁰-dependent pauses may play a role in the regulation of many bacterial promoters.