Function and regulation of the cyanobacterial genes lexA, recA and ruvB: LexA is critical to the survival of cells facing inorganic carbon starvation

Abstract

SummaryThe 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.

Integration of Carbon and Nitrogen Metabolism with Energy Production Is Crucial to Light Acclimation in the CyanobacteriumSynechocystis

“…The existence of such a regulatory network is evident from the regulation of PII, TrxA, and LexA. All three proteins have been shown to regulate enzymes involved in pathways leading to the assimilation of C and N (Lindahl and Florencio, 2003;Domain et al, 2004;Forchhammer, 2004). The main signal inputs appear to be the redox state of PQ, ferredoxin, and H 2 O 2 .…”

“…NtcA is a positive regulator of many genes involved in N assimilation, whereas PII encoded by glnB is considered to be a key sensor of the intracellular C/N ratio (Forchhammer, 2004). LexA has also been shown to regulate genes involved in assimilation of C and N (Domain et al, 2004). Slr2024, a response regulator belonging to the CheY family, has been found to be associated with thylakoid membranes (Wang et al, 2000).…”

Expression and Complementation Analyses of a Chloroplast-Localized Homolog of Bacterial RecA in the MossPhyscomitrella patens

“…10) This suggests that the greater survival rate of the E. coli recA deficient strain transformed with the E. coli recA expression plasmid might be due to the SOS response. The presence of an SOS response in chloroplast is unclear, and cyanobacteria do not have an E. coli-type SOS regulon, 35) suggesting that PpRecA2 is unable to induce the SOS response in E. coli.…”

An AbrB-Like Protein Regulates the Expression of the Bidirectional Hydrogenase in Synechocystis sp. Strain PCC 6803

“…strain ATCC 27152 (27), and Lyngbya majuscula CCAP 1446/4 (23), as well as that of the hydrogenase maturation proteins in Lyngbya majuscula CCAP 1446/4 (15). A LexA-related protein, which has been proposed to not be involved in the classical regulation of DNA repair genes (11), was shown to interact in two different regions of the promoter of the hox genes in Synechocystis sp. strain PCC 6803 (17,28) and was further suggested to activate the transcription of the hox operon (17).…”