Identification and characterisation of ssrA in members of the Helicobacter genus.

Bacterial ssrA encodes tmRNA that functions both as a tRNA and an mRNA to rescue the stalled ribosome on defective mRNAs. In this study, ssrA was identified in four gastric species of Helicobacters and four enterohepatic species of Helicobacters. The tag peptide of 14 amino acids encoded by ssrA showed a pattern of Val(1)Ala(13) in gastric species, a pattern of Ala(1)Val(13 )in enterohepatic species, in contrast to the pattern of Ala(1)Ala(13) in W. succinogenes and C. jejuni, which are closely related to helicobacters. Phylogenetic analysis and the patterns of the tag peptide suggest that the Helicobacter genus could be separated into two genera. High conservation of ssrA in H. pylori was observed. The annotated ORF HP0784 in H. pylori, which largely overlaps ssrA, is unlikely to be functional. H. pylori ssrA interestingly expressed a large and a small tmRNA molecule.