PYRIMIDINE DIMER FORMATION AND REPAIR IN HUMAN-SKIN

Abstract

Cyclobutyl pyrimidine dimers were detected in the DNA of human skin following in vivo irradiation with suberythemal doses of UV radiation from FS-20 sun lamp fluorescent tubes. Dimers were assayed by treatment of extracted DNA with Micrococcus luteus UV-specific endonuclease, alkaline agarose electrophoresis and ethidium bromide staining. This technique, in contrast to conventional dimer assays, can be used with nonradioactive DNA and is optimal at low UV light doses. M. luteus endonuclease-sensitive sites were determined after exposure of untanned skin in 2 volunteers to UV light (0.97, 1.94 or 3.88 .times. 103 J/m2; .lambda., 290-360 nm). At 20 min postirradiation (dose, 1.94 .times. 103 J/m2), fewer M. luteus endonuclease-sensitive sites were found in the DNA than immediately after the irradiation. Even fewer endonuclease-sensitive sites were found at 20 min when the UV-irradiated skin was subsequently irradiated with visible light than when the area was kept in the dark. Some dimer disappearance by excision repair occurs within 20 min of UV irradiation; photoreactivation of dimers can make a contribution to the total repair process. [Failure of repair and/or misrepair of dimers have been implicated as important factors in solar oncogenesis in humans.].