The P1 promoter of the Escherichia coli rpoH gene is utilized by σ70-RNAP or σS-RNAP depending on growth phase

The P1 promoter of the Escherichia coli rpoH gene has been known as a sigma(70)-dependent promoter (RNAP). We show here that it is also recognized by sigma(S). The sigma(70) and sigma(S) RNA polymerase subunits direct transcription from the P1 promoter in the exponential and stationary growth phases, respectively, and transcriptional start sites for the two holoenzymes differ by 1 nt. The transcription after heat shock is sigma(70)-dependent. The results are based on (1) sequence analysis that revealed features of promoters responsive to both, sigma(70)- and sigma(S)-RNAP, (2) in vitro transcription experiments verifying that both holoenzymes are able to transcribe the promoter, (3) electron microscopy results indicating that both holoenzymes bind the same site, (4) primer extension test performed with RNA isolated from the wild-type and rpoS mutant strains, demonstrating that transcription from the P1 promoter in the stationary phase is sigma(S)-dependent. These and previous results point to cooperation of sigma(70), sigma(24), sigma(S) and sigma(54) regulons in the expression of the rpoH gene, coding for the main regulator of the stress response, thus rendering it active in a variety of conditions.