Transformation and Transduction of Escherichia coli: The Nature of Recombinants Formed by Rec, RecF, and λ Red

Abstract

Genetic transformation of Escherichia coli is possible when two requirements are met: (1) the recipient strain lacks exonuclease V, due to a mutation in recB or recC, but has recovered proficiency for recombination by virtue of a second suppressing mutation, sbcA or sbcB; and (2) the uptake of DNA is facilitated by treatment of the recipient cells with CaCl₂ (Oishi and Cosloy, 1972; Wackernagel, 1973). However, compared with other bacteria, the frequency of transformation of E. coli is low, usually about one cell in 10⁶. In an effort to improve this frequency we turned to a source of DNA that is both uniform and enriched for specific markers, namely the specialized transducing variants of phage λ. Our initial observations on transformation by λ gal bio DNA and our efforts to vary its genetic control suggested that certain questions might be approached more readily by studying transduction. We report here observations on transformation and transduction mediated by the RecBC and RecF pathways of E. coli (for review see Clark, 1973) and the Red system of phage λ (for review see Radding, 1973). These experiments have provided an opportunity to examine the properties of recombination mediated by the λ Red system without the possible complications introduced by maturation of phage particles.