Properties of F′ Factor Deoxyribonucleic Acid Transferred from Ultraviolet-Irradiated Donors: Photoreactivation in the Recipient and the Influence of recA, recB, recC , and uvr Genes

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Abstract
Ultraviolet (UV)-irradiated Escherichia coli K-12 F lac + donors transfer damaged F′ factors when mated with female cells. Exposure of the zygotes to white light after mating can cause the photoreactivation of the damaged transferred F′ factors. In so far as the photoreactivation is specific for pyrimidine dimers, these experiments indicate the presence of UV-induced dimers in the transferred F′ factor deoxyribonucleic acid (DNA). These damaged F′ factors are remarkably stable in recA recipients, having a half-life for susceptibility to photoreactivation of 1.5 to 2 hr. This is judged by the formation of Lac + colonies, all of which are male secondary donors. In crosses with wild type and uvrA, recB , or recC mutant recipients, however, the Lac + colonies are predominantly recombinants and photoreactivation is not detected. The extent of DNA synthesis resulting from transfer of F′ episomes from irradiated donors suggests that a complementary strand is formed on the damaged template. Photoreactivation behavior and sedimentation properties are used to deduce properties of such damaged episomes. We conclude that the complementary strand is discontinuous directly opposite dimers in the transferred strand. This structure may be an intermediate in the recombinational event sequence in Rec + recipients.

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