Selective stimulation of one of the mechanisms for genetic recombination of bacteriophage S13.

In certain recombination-deficient (Rec(-)) bacterial strains genetic recombination of bacteriophage S13 is reduced, but the existence of some residual recombination has suggested that there is a secondary mechanism of phage recombination that is still functioning. In these Rec(-)strains it is found that there is no stimulation of recombination by irradiation of the parental phage with ultraviolet light, in contrast to the large increase found when irradiated phage particles infect a Rec(+) host. This selective stimulation of phage recombination in the Rec(+) but not in the Rec(-) strains supports the view that the phage uses at least two mechanisms of genetic recombination.