PROPERTIES OF ACINETOBACTER-CALCOACETICUS RECA AND ITS CONTRIBUTION TO INTRACELLULAR GENE CONVERSION

The Acinetobacter calcoaceticus pcaJ and catJ genes, nearly identical in DNA sequence, differ in transcriptional control and are separated b y more than 20 kb of chromosomal DNA. The pcaJ3125 mutation is repaire d frequently in organisms containing the wild-type catJ gene. This hig h-frequency repair is eliminated in strains lacking the catJ gene, whi ch suggests that recombination between the homologous catJ and pcaJ ge nes contributes to the high-frequency repair of the pcaJ3125 mutation. We report here that the high-frequency repair also requires a functio nal recA gene. The A. calcoaceticus recA gene was cloned in Escherichi a coli by complementation of a recA mutation In the host strain. The n ucleotide sequence of a 1506 bp DNA fragment containing A. calcoacetic us recA was determined. The amino acid sequences of RecA from E. coli and A. calcoaceticus shared 71% identity. The DNA sequences differed i n that a consensus binding site for binding of LexA repressor, represe nted upstream from recA in E. coli, is not evident in the correspondin g region of the A. calcoaceticus DNA sequence. A Tn5 insertion was int roduced into the A. calcoaceticus recA gene. Selection for Tn5-encoded kanamycin resistance allowed the inactivated recA gene to be recombin ed by natural transformation into the A, calcoaceticus chromosome. Str ains that had acquired the mutant gene were sensitive to both MMS and u.v. light, were deficient in natural transformation, and failed to ca rry out catJ-dependent high-frequency repair of the pcaJ3125 mutation.