Induction of pyrimidine dimers and unscheduled DNA synthesis in cultured mouse epitheial cells exposed to 254-nm- and u.v.-B radiation

The induction and fate of pyrimidine dimers and unscheduled DNA synthesis were measured in u.v.-irradiated primary, newborn SENCAR mouse epithelial cells. Unscheduled DNA synthesis was induced in a dose responsive manner by two u.v. sources, a germicidal lamp (254 nm) and an FS4O sunlamp (280–400 nm). Using the endonudease-sensitive site assay to detect pyrimidine dimer production and excision, we examined the response of the newborn mouse cells to both u.v. sources. We were unable to detect the removal of pytimidine dimers with either of the two sources of u.v. The speculation is made that primary, newborn mouse epidennal cells excise u.v.-induced pyrimidine dimers to an extent below the level of detection of the endonudease-sensitive site assay but to an extent sufficient to induce unscheduled DNA synthesis.