Abstract
DIRECT photoreactivation, defined as the repair of ultraviolet irradiated DNA (and hence of DNA-dependent functions) by a light dependent enzymatic reaction, has not previously been demonstrated in any mammal. Biological photoreactivation, or the amelioration of ultraviolet damage to a biological system by subsequent illumination with longer wavelengths, has been described in a few experiments with mammalian cells or whole animals1–3, but the mechanism has been obscure in each of these cases and the possibility of indirect photoreactivation4 has not been ruled out. Previous attempts to demonstrate photoreactivation of growth or of DNA synthesis in cultured mammalian cells have been unsuccessful (refs. 5–7 and unpublished work of J. D. R.), as have attempts to find photoreactivating enzyme activity in a number of mammalian tissues tested in a variety of conditions8.
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