Serologic estimation of thymine dimers in the deoxyribonucleic acid of bacterial and mammalian cells following irradiation with ultraviolet light and postirradiation repair.

The repair of thymine dimers induced by irradiation with ultraviolet light was detected in the DNA of human fibroblast cells, HeLa, but not in the DNA of rat glial or rat pituitary cells. Thymine dimers were detected in the DNA of bacterial and mammalian cells after irradiation with levels of light which are biologically significant, as little as 50 ergs per mmz. The detection of thymine dimers involves the use of specific antibodies to these photoproducts in a radioimmunoassay that can be performed directly on the DNA extracted from the cells. The validity of the assay in the study of repair processes in mammalian cells was first established in a well defined bacterial system. The appearance and excision of thymine dimers in DNA of Bacillus subtilis 101 (an ultraviolet-resistant strain) and B. subtilis 124 (an ultraviolet-sensitive strain which lacks the ability to excise the photoproducts after ultraviolet irradiation) was estimated serologically and was correlated with the transforming activities of the DNA extracted from the cells after irradiation and after a recovery period.