Phage Integration and Chromosome Structure. A Personal History

In 1962, I proposed a model for integration of lambda prophage into the bacterial chromosome. The model postulated two steps (i) circularization of the linear DNA molecule that had been injected into the cell from the phage particle; (ii) reciprocal recombination between phage and bacterial DNA at specific sites on both partners. This resulted in a cyclic permutation of gene order going from phage to prophage. This contrasted with integration models current at the time, which postulated that the prophage was not inserted into the continuity of the chromosome but rather laterally attached or synapsed with it. This chapter summarizes some of the steps leading up to the model including especially the genetic characterization of specialized transducing phages (lambdagal) by recombinational rescue of conditionally lethal mutations. The serendipitous discovery of the conditional lethals is also described.