Transcriptional Regulation of Stress Response and Motility Functions in Helicobacter pylori is Mediated by HspR and HrcA

Department of Biology, University of Bologna, Bologna, Italy, and Molecular Immunology Unit, Novartis Vaccines, Siena, Italy

^* To whom correspondence should be addressed. Email: vincenzo.scarlato{at}unibo.it.

	Abstract

The hrcA and hspR genes of Helicobacter pylori encode two transcriptional repressor proteins that negatively regulate expression of the groES-groEL and hrcA-grpE-dnaK operons. While HspR was previously shown to bind far upstream of the promoters transcribing these operons, the binding sites of HrcA were still to be identified. Here, we demonstrate by footprinting analysis that HrcA binds to operator elements similar to the so-called CIRCE sequences overlapping both promoters. Binding of HspR and HrcA to their respective operators occurs in an independent manner, but the DNA-binding activity of HrcA is increased in the presence of GroESL, suggesting that the GroE chaperonin system co-represses transcription together with HrcA. Comparative transcriptome analysis of the wild type strain versus hspR and hrcA single and double deficient strains revealed that a set of 14 genes is negatively regulated by the action of one or both regulators, while a set of 29 genes is positively regulated. While both positive and negative regulation of transcription by HspR and/or HrcA could be confirmed by RNA primer extension analyses on two representative genes, binding of either regulator to the respective promoters could not be detected, indicating that transcriptional regulation at these promoters involves indirect mechanisms. Strikingly, 14 out of the 29 genes, which were found to be positively regulated by HspR or HrcA, code for proteins involved in flagellar biosynthesis. Accordingly, loss of motility functions was observed for HspR and HrcA single or double mutants. The possible regulatory intersections of the heat shock response and flagellar assembly are discussed.