Modulation ofEscherichia coli RecBCDActivity bythe Bacteriophage XGamandP22AbcFunctions

Plasmids thatexpress thebacteriophage AgamgeneortheP22abc2gene(with andwithout abcl) at controllable levels wereplaced inEscherichia coli andtested foreffects ontheactivity ofRecBCD. LikeGam, Abc2inhibited theATP-dependent exonuclease activity ofRecBCD,apparently notbybinding toDNA. However, Abc2-mediated inhibition waspartial, while Gam-mediated inhibition wascomplete. BothAbc2and Gaminhibited hostsystem-mediated homologous recombination inaChi-containing interval inthechromosomeofahybrid Aphage; Abc2inhibited itmorestrongly thanGam.GambutnotAbc2spared aphage T4 gene2mutant fromrestriction byRecBCD; Abc2exhibited weaksparing activity incombination withAbcl andsubstantial activity incombination withbothAbclandtheP22homologous recombination function Erf. Either Gamorthecombination oftheArecombination functions ExoandBetwassufficient toinduce amode ofplasmid replication thatproduced linear multimers. Thecombination ofAbc2, Abcl, andErfalso exhibited this activity. However, Erfwasinactive, bothbyitself andincombination withAbcl; Abc2hadweakactivity. These results indicate that GamandAbc2modulate theactivity ofRecBCDinsignificantly different ways. In comparison withAGam,P22Abc2hasaweakeffect onRecBCDnuclease activity butastrong effect onits recombination-promoting activity.