SUMMARY: The effects of u.v. irradiation on the survival of and its phage ø11 were studied. The and mutations affected their survival in a similar way to synonymous mutations in . Weigle reactivation (W-reactivation) of ø11 occurred in wild-type and in a mutant but to a lesser extent than has been found for phage λ in Reactivation was -dependent and was accompanied by u.v.-induced mutagenesis in a temperature-sensitive mutant of ø11. Bacterial mutation to streptomycin resistance was induced by u.v. and was also -dependent. In , as in , u.v. was a more effective mutagen in the genetic background. However, a dose-squared response for u.v.-induced mutation of wild-type and strains of to streptomycin resistance, and of a auxotroph to tryptophan independence, was found only with u.v. doses below 1 J m. We suggest that, in relation to the Uvr mechanism of DNA repair, u.v. mutagenesis in involves both repairable and non-repairable lesions. As in , the genetic background reduced the u.v. dose required for maximal W-reactivation of u.v.-irradiated phage. However, there was no enhancement of W-reactivation by post-irradiation broth incubation of Our results are compatible with a non-inducible mechanism for this phenomenon.


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