DNA precipitation assay: a rapid and simple method for detecting DNA damage in mammalian cells.

When mammalian cells are lysed in 2% sodium dodecyl sulphate detergent followed by addition of an equal volume of 0.12 M potassium chloride, a precipitate forms that can be collected by low-speed centrifugation. This precipitate contains the cell protein and nucleic acid in close association with protein. In the absence of DNA damage, most of the DNA precipitates, but when DNA strand breaks are created by exposing cells to ionizing radiation or toxic chemicals, DNA is released from the protein and remains in the supernatant after centrifugation. The proportion of DNA remaining in the supernatant is thus a measure of the amount of DNA damage. This assay is characterized in terms of optimum cell number and pH and dose-response curves for DNA damage and cell survival following ionizing radiation, MNNG, BCNU, and VP-16 are shown. Sensitivity, simplicity, speed, and large sample handling capacity should allow wide application of this new assay to a variety of questions concerning DNA damage and repair.