Indirect Ultraviolet-Reactivation of Phage x (mutagenesis/repair of DNA/bacterial conjugation/Escherichia coli)

When an F- recipient Escherichia coli K12 bacterium receives Hfr or F-lac+ DNA from an ultra- violet-irradiated donor, its capacity to promote DNA repair and mutagenesis of ultraviolet-damaged phage X is sub- stantially increased. We call this phenomenon indirect ultraviolet-reactiva- tion, since its features are essentially the same as those of ultraviolet-reactivation; this repair process occurs in pyrimidine dimer excision-deficient strains and produces clear plaque mutations of the restored phage. Moreover, this process is similar to indirect ultraviolet-induction of prophage X, since it is promoted by conjugation. However, contrarily to indirect induction, it is produced by Hfr donors and occurs in recipients restricting the incoming ultraviolet-damaged donor DNA. The occurrence of indirect ultraviolet-reactivation provides evidence for the existence in E. coli of an inducible error-prone mechanism for the repair of DNA. The survival of ultraviolet (UV)-irradiated phage X is in-