title: Structural and functional characterization of the lexA gene of Xanthomonas campestris pathovar citri.
abstract: The role of the LexA protein and, specifically, its effect on recA expression were analyzed in Xanthomonas campestris pathovar citri (X.c. pv. citri). Overexpression of LexA from X.c. pv. citri, in the plant pathogen, as well as in Escherichia coli, results in increased sensitivity to the DNA-damaging agents mitomycin C and ultraviolet radiation, indicating that the recombinant X.c. pv. citri LexA protein is functional in a different bacterial species. Immunoblot analysis revealed that the overexpressed LexA protein functioned as a repressor of recA expression in X.c. pv. citri, and that the mitomycin C-induced increase in the abundance of RecA was accompanied by specific proteolysis of LexA that required RecA. Although the LexA protein from X.c. pv. citri also blocked the expression of recA in E. coli, the E. coli RecA protein was not able to support the autocatalytic cleavage of LexA from the plant pathogen. The transcription start site of the X.c. pv. citri lexA gene was identified, and the region upstream of this gene was shown to confer responsiveness to mitomycin C on a luciferase reporter gene construct. Electrophoretic mobility-shift assays demonstrated that X.c. pv. citri LexA interacts with the promoter region of X.c. pv. citri lexA, as well as with those of the recA genes of X.c. pv. citri and E. coli. These results indicate that LexA functions as a repressor of gene expression in X.c. pv. citri just as it does in E. coli.
authors.affiliation: Institute of Life Science, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors.forename: Y C
authors.initials: YC
authors.lastname: Yang
authors.forename: M K
authors.initials: MK
authors.lastname: Yang
authors.forename: T T
authors.initials: TT
authors.lastname: Kuo
authors.forename: J
authors.initials: J
authors.lastname: Tu
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D004249:DNA Damage; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D004926:Escherichia coli; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016685:Mitomycin / Q000494:pharmacology; D008969:Molecular Sequence Data; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011938:Rec A Recombinases / Q000235:genetics* / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016959:Xanthomonas campestris / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D016685:Mitomycin; D019384:Nucleic Acid Synthesis Inhibitors; D011938:Rec A Recombinases; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C099195:RecA protein, Xanthomonas campestris