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

The sigma(70) subunit of RNA polymerase plays an essential role in transcription initiation. In addition, sigma(70) has a critical regulatory role during transcription elongation at the bacteriophage lambda late promoter, lambdaP(R). At this promoter, sigma(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 sigma(70) also mediates a pause in early elongation at the lac promoter (plac). Like that at lambdaP(R), the pause at p lac 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 lac stabilizes the interaction between sigma(70) and the remainder of the transcription elongation complex. Bioinformatic analysis suggests that promoter-proximal sigma(70)-dependent pauses may play a role in the regulation of many bacterial promoters.