Identification of the urease operon in Helicobacter pylori and its control by mRNA decay in response to pH

Abstract

SummaryWe investigated the transcription of the urease gene cluster ureABIEFGH in Helicobacter pylori to determine the regulation of gene expression of the highly produced enzyme urease. Northern blot hybridization analysis demonstrated that cells of the wild-type strain grown in an ordinary broth had transcripts of ureAB, ureABI, ureI, ureIE H and ure H FGH, but cells of a ureI-disrupted mutant had only the ureAB transcript. When the wild-type cells were exposed to pH 8 for 30 min, very little mRNA was detected. However, when exposed to pH 6, a large amount of the ureIE H H transcript, which was longer than the ureIE H transcript, together with the additional transcripts ureA-BIEFGH and ure H EFGH were detected. Rifampicin addition experiments demonstrated that urease mRNAs, and the ureIE H transcripts in particular, are more stable at pH 5.5 than at pH 7. In accord with these results, urease activity in the crude cell extract of the pH 5.5 culture was twice as much as that of the pH 7 culture, although the amounts of UreA and UreB detected by immunoblot analysis were similar. The transcription start point of ureI was identified by primer extension using a ureA promoter-deleted mutant, and a consensus sequence of RpoD-RNA polymerase was found in the ureI promoter. The 3 H

Microaerophilic Conditions Permit to Mimic in VitroEvents Occurring during in Vivo Helicobacter pylori Infection and to Identify Rho/Ras-associated Proteins in Cellular Signaling

“…7). This held true at 4 and 24 h, suggesting that enzyme expression is somehow regulated by the less acidic environment in the vicinity of the epithelial cell, in agreement with the observations of Akada et al (39). We could not detect such differences under aerophilic conditions or after incubation of H. pylori with AGS cells grown on plastic.…”

Differential regulation of urease activity in Helicobacter hepaticus and Helicobacter pylori

“…Both urease gene clusters consist of two structural genes (ureAB) and five accessory genes (ureIEFGH) (Beckwith et al, 2001), but the ureB-ureI intergenic distance of H. hepaticus is much shorter (9 bp) than that of H. pylori (200 bp). This indicates that in H. hepaticus there is probably no promoter directly upstream of the ureI gene, thus limiting the possibilities for transcriptional and post-transcriptional regulation (Akada et al, 2000;van Vliet et al, 2001). Furthermore, the overall amino acid sequence of UreI in both species is well conserved, but several amino acid residues which were shown to be required for acid activation of the H. pylori UreI urea channel are absent in the H. hepaticus UreI protein (Weeks et al, 2004).…”

Growth cycle of Helicobacter pylori in gastric mucous layer

“…24 To determine the effect of pH on mRNA decay, the time course after pH shift was analyzed in the presence or absence of rifampicin. 19 In the presence of rifampi cin, transcripts of ureAB, urelE', and ure'FGH were detected even after 60 min at pH 5.5, whereas all tran scripts disappeared at 30min when incubated at pH 7. In the absence of rifampicin, the amount of transcripts after incubation for 60 min at pH 7 was comparable to that at pH 5.5, suggesting that active de novo synthesis and degradation of mRNA is occurring at pH 7.…”