Conjugational recombination in resolvase-deficient ruvC mutants of Escherichia coli K-12 depends on recG.

ruvC mutants of Escherichia coli appear to lack an activity that resolves Holliday intermediates into recombinant products. Yet, these strains produce close to normal numbers of recombinants in genetic crosses. This recombination proficiency was found to be a function of recG. A "mini-kan" insertion in recG was introduced into ruvA, ruvB, and ruvC strains. Conjugational recombination was reduced by more than 100-fold in recG ruvA::Tn10, recG ruvB, and recG ruvC strains and by about 30-fold in a recG ruvA strain carrying a ruvA mutation that is not polar on ruvB. The double mutants also proved very deficient in P1 transduction and are much more sensitive to UV light than ruv single mutants. Since mutation of recG alone has very modest effects on recombination and sensitivity to UV, it is concluded that there is a functional overlap between the RecG and Ruv proteins. However, this overlap does not extend to circular plasmid recombination. The possibility that RecG provides a second resolvase that can substitute for Ruv is discussed in light of these findings.