Calibration of Pulsed Field Gel Electrophoresis for Measurement of DNA Double-strand Breaks

The pulsed field gel electrophoresis (PFGE) assay was calibrated for the measurement of X-ray-induced DNA double-strand breaks in Chinese hamster ovary (CHO) cells. Calibration was conducted by incorporating [125I]deoxyuridine into DNA, which induces one double-strand break for every disintegration that occurs in frozen cells. Based on the percentage of the DNA migrating into the gel, the number of breaks/dalton/Gy was estimated to be (9.3 +/- 1.0) x 10(-12). This value is close to (10 to 12) x 10(-12) determined by neutral filter elution using similar cell lysis procedures at 24 degrees C and at pH 8.0. Also, the estimate is in good agreement with the value of (11.7 +/- 2) x 10(-12) breaks/dalton/Gy as measured in Ehrlich ascites tumour cells using the neutral sucrose gradient method (Blöcher 1988), and (6 to 9) x 10(-12) breaks/dalton/Gy as measured in mouse L and Chinese hamster V79 cells using neutral filter elution (Radford and Hodgson 1985).