Ultraviolet reactivation in bacteriophage lambda.

Abstract

SUMMARY Reactivation of damaged phage λv by recombination with prophage (prophage reactivation) and by u.v. irradiation of host bacteria (u.v. reactivation) were similar in that u.v.- and nitrous acid-damaged phage was reactivated in both, both were eliminated by three rec alleles, neither was much affected by hcr alleles, and both were dependent on the degree of homology between phage and bacterial DNA. These results support a mechanism of u.v. reactivation by recombination between damaged phage DNA and host bacterial DNA. No evidence was obtained to support the hypothesis that u.v. reactivation acts by enhancing host cell reactivation. Prophage reactivation occurred only in bacteria lysogenic for a prophage genetically related to the superinfecting phage λ v and integrated at the gal/bio attachment site. Non-lethal periods of thymine starvation of the host bacteria caused reactivation of u.v.-irradiated phage λ v , comparable with u.v. reactivation.