CLONING AND CHARACTERIZATION OF THE RECA GENE OF PARACOCCUS-DENITRIFICANS AND CONSTRUCTION OF A RECA-DEFICIENT MUTANT

The recA gene of Paracoccus denitrificans has been isolated from a gen omic library by hybridization with the Rhodobacter sphaeroides recA ge ne. Its complete nucleotide sequence consists of 1071 bp encoding a po lypeptide of 356 amino acids. Nucleotide sequence analysis of the P. d enitrificans recA gene revealed the closest identities with the R. sph aeroides and the Rhodobacter capsulatus recA genes. Nevertheless, and surprisingly, recA genes of these two phototrophic bacteria are not DN A damage-inducible when introduced into P. denitrificans cells, wherea s recA genes of both P. denitrificans and Rhizobium etli are. These re sults suggest that the promoters of P. denitrificans and R. etli recA genes have a similar regulatory sequence. A recA-defective mutant of P . denitrificans has also been constructed by replacement of the active recA gene by an in vitro inactivated gene copy.