Helicobacter pylori 5′ ureB-sRNA, a cis-Encoded Antisense Small RNA, Negatively Regulates ureAB Expression by Transcription Termination

Urease is an essential component of gastric acid acclimation by Helicobacter pylori. The increased level of urease in gastric acidity is due, in part, to acid activation of the two-component system consisting of the membrane sensor HP0165 (ArsS) and its response regulator HP0166 (ArsR), which regulates transcription of the seven genes in two separate operons (ureAB and ureIEFGH) of the urease gene cluster. Recently, we identified a novel cis-encoded antisense small RNA, 5' ureB-sRNA, targeted at the 5' end of ureB, which downregulates ureAB expression by truncation of the ureAB transcript at neutral pH. It is not known whether the truncated transcript is due to transcription termination or processing of the full-length mRNA by codegradation of a ureAB mRNA-sRNA hybrid complex. S1 nuclease mapping assays show that the truncated transcript is due to transcription termination. Further studies using an in vitro transcription assay found that 5' ureB-sRNA promotes premature termination of transcription of ureAB mRNA. These results suggest that the antisense small RNA 5' ureB-sRNA downregulates ureAB expression by enhancing transcription termination 5' of ureB. With this mechanism, a limited amount of 5' ureB-sRNA is sufficient to regulate the relatively high level of ureAB transcript.