title: Trans-translation in Helicobacter pylori: essentiality of ribosome rescue and requirement of protein tagging for stress resistance and competence.
abstract: BACKGROUND
  The ubiquitous bacterial trans-translation is one of the most studied quality control mechanisms. Trans-translation requires two specific factors, a small RNA SsrA (tmRNA) and a protein co-factor SmpB, to promote the release of ribosomes stalled on defective mRNAs and to add a specific tag sequence to aberrant polypeptides to direct them to degradation pathways. Helicobacter pylori is a pathogen persistently colonizing a hostile niche, the stomach of humans.
  
  
  RESULTS
  We investigated the role of trans-translation in this bacterium well fitted to resist stressful conditions and found that both smpB and ssrA were essential genes. Five mutant versions of ssrA were generated in H. pylori in order to investigate the function of trans-translation in this organism. Mutation of the resume codon that allows the switch of template of the ribosome required for its release was essential in vivo, however a mutant in which this codon was followed by stop codons interrupting the tag sequence was viable. Therefore one round of translation is sufficient to promote the rescue of stalled ribosomes. A mutant expressing a truncated SsrA tag was viable in H. pylori, but affected in competence and tolerance to both oxidative and antibiotic stresses. This demonstrates that control of protein degradation through trans-translation is by itself central in the management of stress conditions and of competence and supports a regulatory role of trans-translation-dependent protein tagging. In addition, the expression of smpB and ssrA was found to be induced upon acid exposure of H. pylori.
  
  
  CONCLUSIONS
  We conclude to a central role of trans-translation in H. pylori both for ribosome rescue possibly due to more severe stalling and for protein degradation to recover from stress conditions frequently encountered in the gastric environment. Finally, the essential trans-translation machinery of H. pylori is an excellent specific target for the development of novel antibiotics.
authors.affiliation: Institut Pasteur, Unité Postulante de Pathogenèse de Helicobacter, Paris, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Thibonnier
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Thiberge
authors.forename: Hilde
authors.initials: H
authors.lastname: De Reuse
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D016480:Helicobacter pylori / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D009154:Mutation; D018384:Oxidative Stress; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism; D012329:RNA, Bacterial / Q000235:genetics / Q000502:physiology*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D012270:Ribosomes / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D001426:Bacterial Proteins; D011506:Proteins; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins; C430328:small protein B; C096222:tmRNA