The influence of the wavelength of ultraviolet radiation on survival,mutation induction and DNA repair in irradiated chinese hamster cells

Chinese hamster ovary cells were used to compare the cytotoxicity and mutagenicity of far-UV radiation emitted by a low-pressure mercury, germicidal lamp (wavelength predominantly 254 nm) with that of near-UV radiation emitted by a fluorescent lamp with a continuous spectrum (Westinghouse “Sun Lamp”), of which only the radiation with wavelengths greater than 290 nm or greater than 310 nm was transmitted to the cells. The radiation effects were compared on the basis of an equal number of pyrimidine dimers, the predominant lesion induced in DNA by far-UV, for the induction of which much more energy is needed with near-UV than with 254-nm radiation.The numbers of dimers induced were determined by a biochemical method detecting UV-endonuclease-susceptible sites. The equivalence of these sites with pyrimidine dimers was established, qualitatively and quantitatively, in studies with enzymic photoreactivation in vitro and chromatographic analysis of dimers.On the basis of induced dimers, more cells were killed by >310-nm UV than by >290-nm UV; both forms of radiation were more cytotoxic than 254-nm UV when equal numbers of dimers were induced. Moreover, 5–6 times as many mutants were induced per dimer by >310-nm UV than by >290-nm UV; the latter appeared approximately as mutagenic as 254-nm UV. The differences in lethality and mutagenicity were not caused by differences in repair of dimers: cells with an equal number of dimers induced by either 254-nm or near-UV showed the same removal of sites susceptible to a UV endonuclease specific for dimers, as well as an identical amount of repair replication.The results indicate that near-UV induces, besides pyrimidine dimers, other lesions that appear to be of high biological significance.