title: Analysis of the expression of the Rhodobacter sphaeroides lexA gene.
abstract: The regulation of the Rhodobacter sphaeroides lexA gene has been analyzed using both gel-mobility experiments and lacZ gene fusions. PCR-mediated mutagenesis demonstrated that the second GAAC motif in the sequence GAACN7GAACN7GAAC located upstream of the R. sphaeroides lexA gene is absolutely necessary for its DNA damage-mediated induction. Moreover, mutagenesis of either the first or the third GAAC motif in this sequence reduced, but did not abolish, the inducibility of the R. sphaeroides lexA gene. A R. sphaeroides lexA-defective (Def) mutant has also been constructed by replacing the active lexA gene with an inactivated gene copy constructed in vitro. Crude extracts of the R. sphaeroides lexA(Def) strain are unable to form any protein-DNA complex when added to the wild-type lexA promoter of R. sphaeroides. Likewise, the R. sphaeroides lexA(Def) cells constitutively express the recA and lexA genes. All these data clearly indicate that the lexA gene product is the negative regulator of the R. sphaeroides SOS response. Furthermore, the morphology, growth and viability of R. sphaeroides lexA(Def) cultures do not show any significant change relative to those of the wild-type strain. Hence, R. sphaeroides is so far the only bacterial species whose viability is known not to be affected by the presence of a lexA(Def) mutation.
authors.affiliation: Department of Genetics and Microbiology, Autonomous University of Barcelona, Bellaterra, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Tapias
authors.forename: S
authors.initials: S
authors.lastname: Campoy
authors.forename: J
authors.initials: J
authors.lastname: Barbé
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002455:Cell Division / Q000235:genetics; D003001:Cloning, Molecular; D004249:DNA Damage; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D011938:Rec A Recombinases / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics; D012242:Rhodobacter sphaeroides / Q000166:cytology / Q000235:genetics*; D013014:SOS Response, Genetics / Q000235:genetics; D012697:Serine Endopeptidases / Q000235:genetics*; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011938:Rec A Recombinases; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C053139:sulA protein, E coli