Direct evidence that pyrimidine dimers in DNA result in neoplastic transformation.

A specific test for the biological role of UV-induced pyrimidine dimers in DNA is photoreactivation (PR). Fish contain large amounts of the PR enzyme. Portions of cell suspensions of tissue from various organs of the fish Poecilia formosa were exposed to UV radiation (254 nm), then injected into isogenic recipients. An incident fluence of 20 J/m2 resulted in 10% of the fish with large granulomas and 100% with thyroid carcinomas. If the irradiated cell suspension was illuminated with PR light before injection, the yields of both types of lesion were reduced approximately 10-Fold. If the PR light was given before the UV exposure, there was no reduction in the numbers of growths. These experiments show that pyrimidine dimers in DNA can lead to neoplastic transformation.