title: [Characterization of toxin-antitoxin systems in Mycobacterium tuberculosis].
abstract: OBJECTIVE
  To characterize the toxin-antitoxin system (TA system) in Mycobacterium tuberculosis, which consist of MazF homologue gene and its upstream gene.
  
  
  METHODS
  Seven M. tuberculosis MazF homologues were induced alone or co-expressed with their upstream genes respectively in Escherichia coli and Mycobacterium smegmatis, to test the toxic effects of the MazF homologues on bacteria growth, and the antitoxic effects of protein encoded by their upstream genes. The RNA cleavage activity of MazF homologous was identified in vitro with Rv0707 mRNA as the substrate. The promoter region of the identified toxin-antitoxin loci in M. tuberculosis was cloned in front of the lacZ reporter gene in pSD5B vector. The promoter activity was measured under the normal or starvation condition.
  
  
  RESULTS
  The growth of either E. coli or M. smegmatis was inhibited by four MazF homologous proteins, among which Rv1102c, Rv1991c and Rv2801c, but not mtPemK, had the RNA cleavage activities. The toxic effects and RNA cleavage activities of Rv1102c, Rv1991c and Rv2801c were inhibited by their corresponding antitoxin Rv1103c, Rv1991a and Rv2801a, respectively. The other three MazF homologues, Rv1942c, Rv0659c and Rv1495, were not toxic to E. coli and M. smegmatis and also could not cleave RNA. It was found that the promoter activities of Rv2801a-2801c and Rv1991a-1991c systems were significantly increased under the complete starvation condition.
  
  
  CONCLUSIONS
  Our results demonstrated that Rv1103c-1102c, Rv1991a-1991c, Rv2801a-2801c and mtPemI-mtPemK were typical toxin-antitoxin systems in M. tuberculosis. Rv1102c, Rv1991c and Rv2801c were toxin proteins which inhibited cell growth through their RNA cleavage activities, while the mechanism of mtPemK toxin is still unknown. It is possible that Rv2801a-2801c and Rv1991a-1991c systems are involved in the starvation stress response.
authors.affiliation: Key Laboratory for Cell Proliferation and Regulation Biology of Ministry of Education, Institute of Cell Biology, College of Life Sciences, Beijing Normal University, Beijing 100875, China. yiboxian@yahoo.cn
authors.forename: Yibo
authors.initials: Y
authors.lastname: Xian
authors.forename: Lidan
authors.initials: L
authors.lastname: Cui
authors.forename: Junjie
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000992:Antitoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000737:chemistry / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D000992:Antitoxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins