Non-enzymatic DNA strand breaks induced in mammalian cells by fluorescent light.

Fluorescent light (5.4 J . m-2 . s-1) induces 0.041 single-strand breaks per 10(8) daltons per h in the DNA of cultured Chinese hamster cells (4.8 . 10(-6) breaks per 10(8) daltons per J . m-2). The breaks are induced at 1 degrees C and hence are not likely to be the result of endonuclease incision. When the cells are incubated at 37 degrees C, the breaks are rejoined within 2 h. At least two lesions are responsible for the observed effects. One lesion has the ability to break DNA subsequently treated with alkali but is neither toxic nor mutagenic. This lesion is produced by light of wavelength greater than approx. 350 nm. The other lesion(s) produce mutagenicity and/or toxicity, but do not necessarily produce strand breaks. These lesion(s) are produced by light of wavelength less than 350 nm.