The autoregulatory HspR repressor protein governs chaperone gene transcription in Helicobacter pylori

In the present study, we provide evidence that the groESL, hrcA-grpE-dnaK and cbpA-hspR-orf operons encoding the major chaperones of the human gastric pathogen Helicobacter pylori are transcribed by the vegetative sigma factor σ80 and are regulated negatively by the transcriptional repressor HspR. In vitro studies with purified recombinant HspR protein established that the protein represses transcription by binding to large DNA regions centred around the transcription initiation site in the case of the P(cbp) promoter, and around -85 and -120 in the case of the P(gro) and P(hrc) promoters respectively. All three binding sites contain DNA motifs with some similarity to the HAIR sequence identified as a consensus for the HspR protein of Streptomyces. In contrast to the situation in Streptomyces, in which transcription of HspR-regulated genes is induced in response to heat shock, transcription of the HspR-dependent genes in H. pylori is not inducible by thermal stimuli. Transcription of the groESL and cbpA-hspR-orf operons is induced by osmotic shock, while transcription of the hrcA-grpE-dnaK operon, although HspR dependent, is not affected by salt treatment. The possibility that HspR could constitute a global transcriptional regulator for diverse cellular functions with implications for pathogenesis is discussed.