Formation of recombinant lacZ+ DNA in conjugational crosses with a recB mutant of Escherichia coli K12 depends on recF, recJ, and recO.

Conjugational recombination in Escherichia coli was investigated by monitoring synthesis of the lacZ+ product, beta-galactosidase, in crosses between lacZ mutants. We report here that mutation of recB and any combination of recF, recJ, or recO reduces enzyme production by a factor of between 10- and 25-fold whereas mutation of only one of these genes or any combination of recF, recJ, or recO has no more than a 2-fold effect. Mutation of recN has no effect either alone or in combination with the other mutations. We suggest that the products of recF, recJ, and recO may provide an efficient alternative to the RecBCD enzyme for the initiation of recombination in conjugational crosses but that RecBCD activity is needed in this case to produce a viable recombinant product.