Repair and recombination of nonreplicating UV-irradiated phage DNA in E. coli II. Stimulation of RecF-dependent recombination by excision repair of cyclobutane pyrimidine dimers and of other photoproducts.

Three aspects of recombination of UV-irradiated nonreplicating lambda phage DNA were addressed: the photoproduct(s) responsible, the role of UvrABC-mediated excision repair, and the dependence on RecF function. Cyclobutane pyrimidine dimers appeared responsible for some recombination because photoreactivation reduced the frequency of 254-nm-stimulated recombination and because photosensitized 313-nm irradiation stimulated recombination. Other photoproducts seemed recombinogenic as well, because high fluences of 254-nm irradiation stimulated recombination considerably more, per cyclobutane dimer induced, than photosensitized 313-nm irradiation, and because photoreactivation did not eliminate 254-nm stimulated recombination. For both treatments, much, but not all, of the recombination was UvrABC-dependent. Recombination was mostly RecF-dependent, but was not affected by recB recC or recE mutations