Photoreactivation of UV damage in Sminthopsis crassicaudata

Abstract

A comprehensive investigation has been made of photoreactivation of UV damage in cells cultured from the fat-tailed marsupial mouse, Sminthopsis crassicaudata. Maximal photoreversal of the lethal effects of germicidal UV radiation was obtained by exposure of cells to intense fluorescent black light at 37°C. Dose-reduction factors of approximately 2 were obtained. This phenomenon was shown to be a true photoreactive not a photoprotective effect. Attempts to photoreverse the lethal effects of UV light by using white fluorescent light, or black lights at lower temperatures, proved ineffectual. Photoreactivation with black light at 37°C for 30 min effectively photoreversed UV-induced pyrimidine dimers and also substantially reduced the levels of UV-induced DNA-repair replication. Sunlight was also found to be an effective source of photoreactivating light. Although a reasonable correlation was found between the lethal effects of UV light and the number of pyrimidine dimers persisting unrepaired in cellular DNA, some experiments did suggest that either a small subclass of dimers or some type of non-dimer damage contributes significantly to overall lethality. Two of the effects induced by UV light could not, however, be reversed by black light. These were sister-chromatid exchanges and the inhibition of DNA synthesis. The conclusion was reached that either these effects reflect non-dimer (non-photoreactivable damage) or that, under appropriate growth conditions, some damage rapidly disrupts the DNA, say within a replicon, in a manner which cannot be reversed even when the primary lesion has been subsequently removed.