ABORTIVE INDUCTION OF BACTERIOPHAGE P2

Five temperature-sensitive clear-plaque mutants of bacteriophage P2 were isolated, and the properties of strains lysogenic for these mutants were studied. Upon incubation at 42°, all five strains are inactivated and concomitantly lose immunity to superinfection, although at characteristically different rates. In no case, however, is much phage produced, the proportion of productive bacteria varying from 0.1% to 0.5%. The proportion of bacteria producing phage carrying the c allele of the prophage can be increased to 100% by superinfection at 42° with ultraviolet-irradiated wild-type P2. By means of bacterial crosses, it was shown that the temperature-sensitive prophages are able to detach from the bacterial chromosome only if the bacteria are first superinfected. In contrast, it was found that λ prophages, following induction by either temperature shift or ultraviolet irradiation, detach even in the absence of superinfection. The derepression of at least one P2 prophage gene following incubation at 42° was clearly demonstrated. A strain lysogenic for a temperature-sensitive clear mutant, blocked also in this gene, was found to be inactivated much more slowly at 42°, although the immunity of the strain was lost at the rate characteristic of that particular clear mutant. © 1968.