title: Function and regulation of the cyanobacterial genes lexA, recA and ruvB: LexA is critical to the survival of cells facing inorganic carbon starvation.
abstract: The cyanobacterial genes lexA, recA and ruvB were analysed in Synechocystis PCC6803, which is shown here to be more radiation resistant than the other unicellular model strain Synechococcus PCC7942. We found that cyanobacteria do not have an Escherichia coli-type SOS regulon. The Synechocystis lexA and recA promoters were found to be strong and UV insensitive, unlike the ruvB promoter, which is weak and UV-C inducible. Yet, lexA and recA are regulated by UV-C, but the control is negative and occurs at the post-transcriptional level. Two novel conserved elements were characterized in the lexA promoter: (i) an unusually long crucial box 5'-TAAAATTTTGTATCTTTT-3' (-64, -47); and (ii) a negatively acting motif 5'-TAT GAT-3' (-42, -37). These elements were not found in the recA promoter, which appeared to be unusually simple in harbouring only a single crucial element (i.e. the canonical -10 box). RuvB, operating in recombination-dependent cellular processes, was found to be dispensable to cell growth, whereas LexA and RecA appeared to be critical to cell viability. Using DNA microarrays, we have identified 57 genes with expression that is altered, at least twofold, in response to LexA depletion. None of these genes is predicted to operate in DNA metabolism, arguing against the involvement of LexA in the regulation of DNA repair. Instead, most of the LexA-responsive genes were known to be involved in carbon assimilation or controlled by carbon availability. Consistently, the growth of the LexA-depleted strain was found to be strongly dependent on the availability of inorganic carbon.
authors.affiliation: Service de Biochimie et Génétique Moléculaire,91191 Gif sur Yvette Cedex, France.
authors.forename: Francis
authors.initials: F
authors.lastname: Domain
authors.forename: Laetitia
authors.initials: L
authors.lastname: Houot
authors.forename: Franck
authors.initials: F
authors.lastname: Chauvat
authors.forename: Corinne
authors.initials: C
authors.lastname: Cassier-Chauvat
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism* / Q000502:physiology*; D000458:Cyanobacteria / Q000235:genetics* / Q000502:physiology; D004249:DNA Damage; D004260:DNA Repair; D015964:Gene Expression Regulation, Bacterial; D011401:Promoter Regions, Genetic; D011938:Rec A Recombinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics; D013014:SOS Response, Genetics; D012697:Serine Endopeptidases / Q000378:metabolism* / Q000502:physiology; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D011938:Rec A Recombinases; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C061260:RuvB protein, Bacteria