Recombination-Promoting Activity of the Bacteriophage λ Rap Protein in Escherichia coli K-12

The rap gene of bacteriophage λ was placed in the chromosome of an Escherichia coli K-12 strain in which the recBCD gene cluster had previously been replaced by the λ red genes and in which the recG gene had been deleted. Recombination between linear double-stranded DNA molecules and the chromosome was tested in variants of the recGΔ red(+) rap(+) strain bearing mutations in genes known to affect recombination in other cellular pathways. The linear DNA was a 4-kb fragment containing the cat gene, with flanking lac sequences, released from an infecting phage chromosome by restriction enzyme cleavage in the cell. Replacement of wild-type lacZ with lacZ::cat was monitored by measuring the production of Lac-deficient chloramphenicol-resistant bacterial progeny. The results of these experiments indicated that the λ rap gene could functionally substitute for the E. coli ruvC gene in Red-mediated recombination.