The effect of UV irradiation on the capacity of an Hfr recA strain of Escherichia coli to act as donor

Summary The ability of a recA Hfr strain of Escherichia coli to form colonies is extremely sensitive to inhibition by ultraviolet light (Fig. 2). Furthermore, in this strain the synthesis of DNA is stopped completely by a dose of 385 ergs/mm² of UV (Fig. 3). Nevertheless, the ability of this recA Hfr strain to act as a donor in sexual recombination was no more sensitive to UV than that of a wild type donor (Fig. 1). Furthermore, when irradiated and mated with a recA female, in which DNA synthesis was also inhibited by UV (Fig. 3), there was a net synthesis of DNA as measured by the incorporation of C¹⁴ thymidine (Fig. 4). By using nalidixic acid resistant recA donors and recipients in all combinations, irradiating with UV and treating with nalidixic acid during mating, it is shown that DNA was synthesized by the donor (Fig. 5). It is concluded that synthesis of DNA directed by the sex factor during mating in a recA donor is not as sensitive to inhibition by UV as normal DNA synthesis in a recA donor.