Specialized transduction with λplac5: Dependence on recA and on configuration of lac and attλ

The construction of λplac5 transducing phages carrying various lacZ alleles is described. Genetically disabled (N^- N^- P^-) λplac transducing phages were used to study the dependence of specialized transduction on host RecA function and on the location of the lacZ gene in the recipient strain. In the absence of site-specific recombination at attλ, transduction was completely dependent on host RecA function. Regardless of the configuration of attλ, λplac transducing phages recombined at a 20- to 50-fold higher frequency with F42lac than with a lac gene located in the cellular chromosome. Deletion mutants of lacZ in the recipient strain were used to show that the probability of lac recombination resulting from λplac infection is apparently proportional to the amount of homology between the parental lacZ genes.