Dna Single‐strand Lesions Due to ‘Sunlight’ and Uv Light: A Comparison of Their Induction in Chinese Hamster and Human Cells, and Their Fate in Chinese Hamster Cells

It has been shown that the lethal properties of germicidal UV light (254 nm) and sunlight‐simulating near UV light are qualitatively different (Elkind et al., 1978). Further to compare these two radiations, the induction of single‐strand DNA breaks (i.e. frank breaks plus alkali‐labile lesions) was measured in two cell lines. Equal numbers of breaks in Chinese hamster cells require a dose of UV 5.5% of a near UV dose but in HeLa cells a UV dose of 7.6% of a near‐UV dose is required. The rate of break production by these radiations is about 1/10‐th of that due to X‐rays when a comparison is made on an equal killing dose basis. The inventory of breaks in Chinese hamster cells was also followed and was found to be characteristically different for UV compared to near UV light. These data indicate that significant differences exist, at a molecular level, in the effects produced by ultraviolet and sunlight‐simulating light, and further emphasize the need for caution in attempting to extrapolate from observed molecular or biological effects due to the former to those to be expected from the latter.