Production of pyrimidine dimers in DNA of human skin exposed in situ to UVA radiation

Cyclobutyl pyrimidine dimers, measured as sites recognized by the dimer-specific ultraviolet (UV) endonuclease from Micrococcus luteus, were produced in DNA of human skin exposed in situ to UVA (320-400 nm) radiation. The dimer yields produced by a broadband UVA source, by broadband UVA filtered to remove all light of wavelength less than 340 nm, and by narrow band radiation centered at 365 nm were similar, indicating that UVA radiation, and not stray shorter wavelength radiation, was responsible for dimer production. The identity of the UVA-induced DNA lesions was confirmed as pyrimidine dimers by photoreactivation of approximately 100% of the endonuclease-sensitive sites in vitro with the 40,000 dalton Escherichia coli photoreactivating enzyme.