The timing of erf-mediated recombination in replication, lysogenization, and the formation of recombinant progeny by Salmonella phage P22.

Following infection, the development of phage P22 by either the lytic or the lysogenic pathways requires recombination, mediated either by the phage erf system or by the bacterial ret system [Botstein, D., and Matz, M. J. (1970) J. Mol. Biol. 54, 417-4401. We have investigated the timing of the essential recombinational processes with temperature-shift experiments using a temperature-sensitive erf mutant. In retcells, erf function appears to be required early in the infection to complete some essential step, the timing of which is the same in both the lytic and lysogenic circumstances. Once the step has taken place, subsequent development can occur without further erf function. However, the bulk of recombinant progeny arising in lytic crosses in retcells result from nonessential erf action late in the infection, after the time of the required early step.