Sensitivity of DNA synthetic phase to near-ultraviolet radiation: chromatid damage at early and late replication periods.

Syrian hamster embryo (SHE) cells were pulse-labeled with bromodeoxyuridine at various periods of the S-phase, and then irradiated with near ultraviolet (NUV) light. Observation of the radiated chromosomes in the subsequent metaphase stage revealed that the period between the second and fourth hour of the S-phase is most sensitive to radiation damage. The prevalent types of chromatid aberrations are 'gaps' and 'breaks'. The results strongly suggest that the detrimental effect of NUV-radiation on chromosomes depends primarily on the particular stage when radiation is applied.