Recombination in Bacteriophage Lambda I. Exchange of DNA Promoted by Phage and Bacterial Recombination Mechanisms

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It has been found that recombination in bacteriophage λ is accompanied by material exchange of DNA (Meselson and Weigle, 1961; Kellenberger, Zichichi, and Weigle, 1961) and occurs by breakage and reunion of the participating chromosomes (Meselson, 1964). Since these earlier reports, however, several recombination systems for λ have been discovered: the int system, in which recombination at a specific site is promoted by a λ gene product (Echols, Gingery, and Moore, 1968; Weil and Signer, 1968); the red system, which is also under the control of λ gene products (Echols and Gingery, 1968; Signer and Weil. 1968); and the rec system, which is directed by bacterial genes (Echols and Gingery, 1968; Signer and Weil, 1968). The red and rec recombination systems, unlike the int , are not site specific and seem to be responsible for all general recombination in λ . Since the physical exchange of DNA has been studied so far only when all the three systems were working together, we repeated some of the earlier experiments for each system separately, using the appropriate int , red , or rec mutants. We find that recombination promoted by each system involves material exchange. MATERIALS AND METHODS Bacterial Strains Escherichia coli C600 su + (obtained from F. Jacob) was used for making phage stocks and for phage titration. A C600 thy − mutant was selected (Stacey and Simson, 1965) for the preparation of 3 H-Iabeled stocks. E. coli 28 and 152, obtained from M. Gottesman, were used for the phage crosses (Gottesman and Yarmolinsky, 1968). They are su − rec + ...