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

Abstract

The P1 promoter of the Escherichia coli rpoH gene has been known as a σ70-dependent promoter (RNAP). We show here that it is also recognized by σS. The σ70 and σS 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 σ70-dependent. The results are based on (1) sequence analysis that revealed features of promoters responsive to both, σ70- and σS-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 σS-dependent. These and previous results point to cooperation of σ70, σ24, σS and σ54 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. © 2008 Federation of European Microbiological Societies.