Repair of UV-damage in single stranded DNA : different roles of UVR and REC systems of E. Coli in UV reactivation of phage OX174

Ultraviolet (UV) reactivation is the increased survival of a UV-irradiated phage population as a result of pre-irradiation of the host cells. The extent of this repair phenomenon in bacteriophage OX174 and the influence of various enzymatic apparata of the host cells on such repair has been investigated, the special point of interest being the single-strandedness of OX-DNA which is unable to act as a template for the well known excision repair mechanism. It was observed that for maximum amount of reactivation, the necessary radiation dose on the phage was constant (approximately 1000 ergs/mm2 at 254 mu) for different bacterial strains while the doses on the host cells varied between 100-500 ergs/mm2, depending on their genetic make up. In the case of uvr (excision-defective) strains, a dose of 100 ergs/mm2 enabled them to give a maximum reactivation factor of 4, while there was no reactivation with rec (recombination-deficient) strains for any dose, high or low. (author)