[Cytogenetic effect of ultraviolet rays in mammalian cells at the DNA synthesis stage].

The frequency of chromosome aberrations induced by UV light at various wavelengths in the primary culture of mouse embryonic fibroblasts during the S-phase was studied. The aberration frequency is wavelength-dependent and reaches a maximum at 265 nm. The action spectrum for the chromosome aberrations determined at 254, 265, 280 and 302 nm closely conforms to the absorption spectra of thymidine. The value of caffeine potentiation was the same for 265 and 280 nm UV-induced aberrations. This indicates that primary chromosome damages and their transformation in cells are similar at these two wavelengths. The data obtained suggest that the formation of DNA cross-links following thymine dimerization is the first step in the formation of UV-induced chromosome aberrations in mammalian cells at the S phase.