Photoreactivation of RNA in UV-irradiated insect eggs (Smittia sp., Chironomidae, Diptera) II. Evidence for heterogeneous light-dependent repair activities

Abstract. Two biological effects of UV radiation upon Smittia eggs are observed, both of which seem to be associated with the formation of pyrimidine dimers in the RNA (largely ribosomal) of the eggs. While irradiation of the anterior pole region causes the formation of an aberrant segment pattern (double abdomen induction), irradiation of entire eggs leads to an arrest of their development (inactiva-tion). Both UV effects are photoreversible with different action spectra of the photoreactivating light. A dose rate dependence of the photoreactivation can be observed after both UV effects. The saturating dose rate is about 6 W/m² (at 440 nm) after UV induction of double abdomens. Upon UV inactivation, the saturating dose rate level for the photoreactivating light is much higher, and a single light flash causes both a considerable biological reactivation and the disappearance of about 7 × 10⁹ pyrimidine dimers from the total RNA per egg. The results indicate the presence of heterogeneous light-dependent repair activities acting upon UV induced pyrimidine dimers in the RNA of the eggs.