Single-strand scission and repair of DNA in mammalian cells by bleomycin.

DNA single-strand breakage by bleomycin treatment of cultured mammalian cells was demonstrated by the method of alkaline elution. Elution patterns from treated L1210 cells indicated that part of the DNA was extensively broken while the remainder was affected to a lesser degree. This biphasic effect, which was less prominent in human fibroblasts, may reflect a selective sensitivity either of part of the cell population or of part of the DNA within individual cells. In both cell types, the DNA damage was at least partially repaired upon incubation of the cells after removal of drug. Bleomycin did not inhibit the rejoining of X-ray-induced single-strand breaks. The production and repair of DNA single-strand breaks after bleomycin treatment were the same in normal human and xeroderma pigmentosum fibroblasts, indicating that these events do not require the excision endonuclease that appears to be defective in these ultraviolet light-sensitive xeroderma cells.