RECB RECJ MUTANTS OF SALMONELLA-TYPHIMURIUM ARE DEFICIENT IN TRANSDUCTIONAL RECOMBINATION, DNA-REPAIR AND PLASMID MAINTENANCE

recB recJ mutants of Salmonella typhimurium are deficient in transduct ion of chromosomal markers and ColE1-derived plasmids, and also in the maintenance of ColE1 and F plasmids. Plasmid instability is less seve re in recD recJ strains; ColE1 plasmid DNA preparations from these str ains show an increased yield of high molecular weight (HMW) linear mul timers and a concomitant reduction in plasmid monomers compared to the wild type. Plasmids remain unstable in recA recD recJ mutants; since these do not produce HMW linear concatemers, we propose that a decreas e in monomer production leads to plasmid instability, recB recJ strain s also display decreased viability, a component of which may be relate d to their deficiency in DNA repair. In contrast to their severe defec ts in recombination, DNA repair and plasmid maintenance, recB recJ mut ants of S. typhimurium behave similarly to the wild type in the segreg ation of chromosome duplications, The latter observation suggests that neither RecBCD nor RecJ functions are required for chromosomal recomb ination events that do not involve the use of free ends as recombinati on substrates.