title: Geobacter sulfurreducens has two autoregulated lexA genes whose products do not bind the recA promoter: differing responses of lexA and recA to DNA damage.
abstract: The Escherichia coli LexA protein was used as a query sequence in TBLASTN searches to identify the lexA gene of the delta-proteobacterium Geobacter sulfurreducens from its genome sequence. The results of the search indicated that G. sulfurreducens has two independent lexA genes designated lexA1 and lexA2. A copy of a dinB gene homologue, which in E. coli encodes DNA polymerase IV, is present downstream of each lexA gene. Reverse transcription-PCR analyses demonstrated that, in both cases, lexA and dinB constitute a single transcriptional unit. Electrophoretic mobility shift assays with purified LexA1 and LexA2 proteins have shown that both proteins bind the imperfect palindrome GGTTN(2)CN(4)GN(3)ACC found in the promoter region of both lexA1 and lexA2. This sequence is also present upstream of the Geobacter metallireducens lexA gene, indicating that it is the LexA box of this bacterial genus. This palindrome is not found upstream of either the G. sulfurreducens or the G. metallireducens recA genes. Furthermore, DNA damage induces expression of the lexA-dinB transcriptional unit but not that of the recA gene. However, the basal level of recA gene expression is dramatically higher than that of the lexA gene. Likewise, the promoters of the G. sulfurreducens recN, ruvAB, ssb, umuDC, uvrA, and uvrB genes do not contain the LexA box and are not likely to bind to the LexA1 or LexA2 proteins. G. sulfurreducens is the first bacterial species harboring a lexA gene for which a constitutive expression of its recA gene has been described.
authors.affiliation: Department of Genetics and Microbiology, Universitat Autònoma de Barcelona, Spain.
authors.forename: Mónica
authors.initials: M
authors.lastname: Jara
authors.forename: Cinthia
authors.initials: C
authors.lastname: Núñez
authors.forename: Susana
authors.initials: S
authors.lastname: Campoy
authors.forename: Antonio R
authors.initials: AR
authors.lastname: Fernández de Henestrosa
authors.forename: Derek R
authors.initials: DR
authors.lastname: Lovley
authors.forename: Jordi
authors.initials: J
authors.lastname: Barbé
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D016384:Consensus Sequence; D004249:DNA Damage; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D015870:Gene Expression; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D020560:Proteobacteria / Q000235:genetics*; D011938:Rec A Recombinases / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D019951:DNA Polymerase beta; D004268:DNA-Binding Proteins; D011938:Rec A Recombinases; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein