Repair of Cyclobutane Dimers and (6–4) Photoproducts in Icr 2a Frog Cells

The removal of cyclobutane dimers and Pyr(6–4)Pyo photoproducts from the DNA of UV‐irradiated ICR 2A frog cells was determined by radioimmunoassay. In the absence of photoreactivat‐ing light, 15% of the cyclobutane dimers and 60% of the (6–4) photoproducts were removed 24 h post‐irradiation with 10 J m −2 , Exposure to 30 kJ m −2 photoreactivating light resulted in removal of 80% of the cyclobutane dimers and an enhanced rate of repair of (6–4) photoproducts, resulting in a loss of 50% of these lesions in 3 h. The preferential removal of (6–4) photoproducts by excision repair resembles previously published data for mammalian cells.