Effects of radiation on the survival of excision-defective cells from Drosophila melanogaster.

The effect of various doses of ultraviolet light and ionizing radiation on the survival of excision-defective Drosophila cells has been determined by cloning treated and untreated cells in agarose. Although excision-defective cells survive moderate amounts of DNA damage, they display a severe hypersensitivity to both types of radiation relative to excision-proficient cells. Exposure of ultraviolet-irradiated cells to fluorescent light results in a reduction of the density of pyrimidine dimers in cellular DNA and a 10-to 20-fold increase in survival. Parallel analysis of dimer density and survival, however, suggests that much of the lethal effect of ultraviolet light is due to nondimer damage. Cell proliferation was monitored in both excision-proficient and excision-defective cells exposed to doses of ultraviolet light that reduced survival by 90%. Under these conditions excision-proficient cells displayed exponential growth whereas excision-defective cells exhibited no cell proliferation for 12 days.