title: Rhodobacter sphaeroides LexA has dual activity: optimising and repressing recA gene transcription.
abstract: Transcription of the Rhodobacter sphaeroides recA promoter (P(recA)) is induced upon DNA damage in a lexA-dependent manner. In vivo experiments demonstrate that LexA protein represses and might also activate transcription of P(recA). Purified R.sphaeroides LexA protein specifically binds the SOS boxes located within the P(recA) region. In vitro transcription analysis, using Escherichia coli RNA polymerase (RNAP), indicated that the presence of LexA may stimulate and repress transcription of P(recA). EMSA and DNase I footprinting experiments show that LexA and RNAP can bind simultaneously to P(recA). At low LexA concentrations it enhances RNAP binding to P(recA), stimulates open complex formation and strand separation beyond the transcription start site. At high LexA concentrations, however, RNAP-promoted strand separation is not observed beyond the +5 region. LexA might repress transcription by interfering with the clearance process instead of blocking the access of RNAP to the promoter region. Based on these findings we propose that the R.sphaeroides LexA protein performs fine tuning of the SOS response, which might provide a physiological advantage by enhancing transcription of SOS genes and delaying full activation of the response.
authors.affiliation: Departamento de Genética y Microbiología, Universitat Autónoma de Barcelona, Bellaterra, 08193 Barcelona, Spain.
authors.forename: Angels
authors.initials: A
authors.lastname: Tapias
authors.forename: Silvia
authors.initials: S
authors.lastname: Fernández
authors.forename: Juan C
authors.initials: JC
authors.lastname: Alonso
authors.forename: Jordi
authors.initials: J
authors.lastname: Barbé
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D046911:Macromolecular Substances; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000235:genetics*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004247:DNA; D012321:DNA-Directed RNA Polymerases; D046911:Macromolecular Substances; D011938:Rec A Recombinases; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein