Photorepair of ultraviolet radiation-induced pyrimidine dimers in corneal DNA

The induction and photorepair of pyrimidine dimers in DNA have been measured in the ultraviolet-irradiated, corneal epithelium of the marsupial, Monodelphis domestica, using damage-specific nucleases from Micrococcus luteus in conjunction with agarose gel electrophoresis. We observed that FS-40 sunlamps (280–400 nm) induced 7.2 ± 1.0 × 10⁻⁵ pyrimidine dimers per kilobase (kb) of DNA per J/m². Following 100 J/m², 50% and > 90% of the dimers were photorepaired during a 10- and 30-min exposure to photoreactivating light (320–400 nm), respectively. In addition ∼ 70% and ∼ 60% of the dimers induced by 300 and 500 J/m², respectively, were repaired by a 60-min exposure to photoreactivating light. The capacity of the corneal epithelium of M. domestica to photorepair pyrimidine dimers identifies this animal as a potentially useful model withwhich to determine whether pyrimidine dimers are involved in pathological changes of the irradiated eye.