MUTATION OF RECF, RECJ, RECO, RECQ, OR RECR IMPROVES HFR RECOMBINATION IN RESOLVASE-DEFICIENT RUV RECG STRAINS OF ESCHERICHIA-COLI

The formation of recombinants in Hfr crosses was studied in Escherichi a coli strains carrying combinations of genes known to affect recombin ation and DNA repair. Mutations in ruv and recG eliminate activities t hat have been shown to process Holliday junction intermediates by nucl ease cleavage and/or branch migration. Strains carrying null mutations in both ruv and recG produce few recombinants in Hfr crosses and are extremely sensitive to UV light. The introduction of additional mutati ons in recF, recJ, recO, recQ, or recR is shown to increase the yield of recombinants by 6- to 20-fold via a mechanism that depends on recBC . The products of these genes hare been linked with the initiation of recombination. We propose that mutation of recF, recJ, recO, recQ, or recR redirects recombination to events initiated by the RecBCD enzyme. The strains constructed were also tested for sensitivity to UV light. Addition of recF, recJ, recN, recO, recQ, or recR mutations had no ef fect on the survival of ruv recG strains. The implications of these fi ndings are discussed in relation to molecular models for recombination and DNA repair that invoke different roles for the branch migration a ctivities of the RuvAB and RecG proteins.