title: Mycobacterium tuberculosis possesses an unusual tmRNA rescue system.
abstract: Trans-translation is a key process in bacteria which recycles stalled ribosomes and tags incomplete nascent proteins for degradation. This ensures the availability of ribosomes for protein synthesis and prevents the accumulation of dysfunctional proteins. The tmRNA, ssrA, is responsible for both recovering stalled ribosomes and encodes the degradation tag; ssrA associates and functions with accessory proteins such as SmpB. Although ssrA and smpB are ubiquitous in bacteria, they are not essential for the viability of many species. The Mycobacterium tuberculosis genome has homologues of both ssrA and smpB. We demonstrated that ssrA is essential in M. tuberculosis, since the chromosomal copy of the gene could only be deleted in the presence of a functional copy integrated elsewhere. However, we were able to delete the proteolytic tagging function by constructing strains carrying a mutant allele (ssrADD). This demonstrates that ribosome rescue by ssrA is the essential function in M. tuberculosis, SmpB was not required for aerobic growth, since we were able to construct a deletion strain. However, the smpBΔ strain was more sensitive to antibiotics targeting the ribosome. Strains with deletion of smpB or mutations in ssrA did not show increased sensitivity (or resistance) to pyrazinamide suggesting that this antibiotic does not directly target these components of the tmRNA tagging system.
authors.affiliation: Queen Mary University of London, Barts & The London School of Medicine and Dentistry, London E1 2AT, UK.
authors.forename: Yoann
authors.initials: Y
authors.lastname: Personne
authors.affiliation: Queen Mary University of London, Barts & The London School of Medicine and Dentistry, London E1 2AT, UK. Electronic address: t.parish@qmul.ac.uk.
authors.forename: Tanya
authors.initials: T
authors.lastname: Parish
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D050296:Microbial Viability; D009169:Mycobacterium tuberculosis / Q000378:metabolism / Q000502:physiology*; D014176:Protein Biosynthesis / Q000502:physiology*; D012329:RNA, Bacterial / Q000096:biosynthesis* / Q000502:physiology; D016601:RNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D012270:Ribosomes / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins; C430328:small protein B; C096222:tmRNA
keywords: Essential genes; Mycobacterium tuberculosis; Pyrazinamide; Ribosome rescue; Trans-translation