RESOLUTION OF HOLLIDAY INTERMEDIATES IN RECOMBINATION AND DNA-REPAIR - INDIRECT SUPPRESSION OF RUVA, RUVB, AND RUVC MUTATIONS

The ruvA, ruvB, and ruvC genes of Escherichia coli provide activities that catalyze branch migration and resolution of Holliday junction int ermediates in recombination. Mutation of any one of these genes interf eres with recombination and reduces the ability of the cell to repair damage to DNA. A suppressor of ruv mutations was identified on the bas is of its ability to restore resistance to mitomycin and UV light and to allow normal levels of recombination in a recBC sbcBC strain carryi ng a Tn10 insertion in ruvA. The mutation responsible was located at 1 2.5 min on the genetic map and defines a new locus which has been desi gnated rus. The rus suppressor works just as well in recBC sbcA and re c+ sbc+ backgrounds and is not allele specific. Mutations in ruvB and ruvC are suppressed to an intermediate level, except when ruvA is also inactive, in which case suppression is complete. In all cases, suppre ssion depends on RecG protein, a DNA-dependent ATPase that catalyzes b ranch migration of Holliday junctions. The rus mutation activates an a dditional factor that probably works with RecG to process Holliday jun ction intermediates independently of the RuvAB and RuvC proteins. The possibility that this additional factor is a junction-specific resolva se is discussed.