Determination of the Paracoccus denitrificans SOS box

By gel retardation experiments with crude cell extracts of Paracoccus denitrificans it was demonstrated that a protein specifically binds to the promoter of the P. denitrificans recA gene. PCR mutagenesis of the recA promoter showed that the GAACN7GAAC motif is required for the formation of the DNA-protein complex. This protein also binds to the GTTCN7GTTC motif, which is present in the promoter of the P. denitrificans uvrA gene. Mutational analysis of the promoter regions of both P. denitrificans recA and uvrA genes indicated that the GAACN7GAAC and GTTCN7GTTC sequences are required for DNA-damage-mediated induction of these two genes in vivo. Furthermore, the P. denitrificans recA gene was DNA-damage-inducible when introduced into cells of the phylogenetically related phototrophic bacterium Rhodobacter sphaeroides, although this inducibility was lost in mutants in the GAACN7GAAC motif. These results indicate that P. denitrificans possesses the same SOS box as R. sphaeroides, which, in agreement with previous work, is proposed as being the GTTCN7GTTC motif.