Heteroduplex chain polarity in recombination of phage λ by the Red, RecBCD, RecBC(D(⁻)) and RecF pathways

Abstract

We have examined the chain polarity of heteroduplex DNA in unreplicated, bacteriophage λ splice recombinants when recombination was by the RecBCD, RecBC(D(⁻)), or RecF pathway of Escherichia coli or the Red pathway of λ. For each of these pathways, recombination is activated by the cutting of cos that accompanies chromosome packaging, and is effected by recombination enzymes acting at the right end created by that cutting. For exchanges occurring near cos, one parent makes a lesser physical and genetic contribution than does the other. For each pathway, when the phage carried standard cos, this minority contribution was predominantly on the r chain, ending 5' at the right end of λ. When standard cos was replaced by a cloned inverted cos located centrally on the standard λ genetic map, minority contribution was predominantly on the l chain. In each case, the polarity of the overlap was usually that formed by 3' overhangs of parental information and material. These results are discussed in the context of current models of recombination for the different pathways.