Red-Mediated Recombination in Bacteriophage Lambda

Abstract

Among unreplicated encapsidated lambda chromosomes “crossovers” are nonuniformly distributed along the chromosome (Jordan and Mesleson, 1965). They are concentrated at the ends, especially the right end (Fig. 1). Among replicated chromosomes, however, crossovers are uniformly distributed as judged from the congruity of the linkage map and the microscopically examined chromosome (Fig. 2). The explanation for this difference between replicated and unreplicated chromosomes is that recombination throughout lambda, except at the ends, is dependent on extensive DNA synthesis (Stahl et al., 1972a). The dependence of recombination on synthesis and the resulting nonuniform crossover distribution along unreplicated chromosomes is conspicuous only in the presence of the Red system, the general recombination system of the phage (Stahl et al., 1974).