W reactivation is inefficient in repair of the bacterial chromosome.

UV-inducible "SOS" processes associated with W reactivation of phage lambda were studied for their effect on repair of lambda prophage integrated in the bacterial chromosome. For this purpose, lambda c1857 ind red-lysogens were used. These lysogens, although non-inducible by UV light, can be induced by raising the temperature from 30 degrees to 42 degrees. If the W reactivation processes are involved in repair of the bacterial DNA, when the lysogens are incubated at 30 degrees after UV exposure W reactivation should be fully expressed and should also exert an effect on the bacterial chromosome and the prophage inside it. When heat-induction is delayed until the time at which W reactivation reaches its maximum, a considerable increase in phage survival might then be expected. The results presented in this report show, however, that the delayed induction had only a small effect on the survival of prophage in the wild-type strain (possibly attributable to excision repair) and no detectable effect on prophage in a uvrA strain. From these results we conclude that W reactivation is largely irrelevant to the repair of UV-damaged bacterial DNA.