MOLECULAR-CLONING, SEQUENCE AND REGULATION OF EXPRESSION OF THE RECA GENE OF THE PHOTOTROPHIC BACTERIUM RHODOBACTER-SPHAEROIDES

The recA gene of Rhodobacter sphaeroides 2.4.1 has been isolated by co mplementation of a UV-sensitive RecA(-) mutant of Pseudomonas aerugino sa. Its complete nucleotide sequence consists of 1032 bp, encoding a p olypeptide of 343 amino acids. The deduced amino acid sequence display ed highest identity to the RecA proteins from Rhizobium meliloti, Rhiz obium phaseoli, and Agrobacterium tumefaciens. An Escherichia coli-lik e SOS consensus region, which functions as a binding site for the LexA repressor molecule was not present in the 215 bp upstream region of t he R. sphaer oides recA gene. Nevertheless, by using a recA-lacZ fusio n, we have shown that expression of the recA gene of R. sphaeroides is inducible by DNA damage. A recA-defective strain of R. sphaeroides wa s obtained by replacement of the active recA gene by a gene copy inact ived in vitro. The resulting recA mutant exhibited increased sensitivi ty to UV irradiation, and was impaired in its ability to perform homol ogous recombination as well as to trigger DNA damage-mediated expressi on. This is the first recA gene from a Gram-negative bacterium that la cks an E. coli-like SOS box but whose expression has been shown to be DNA damage-inducible and auto-regulated.