CHEF electrophoresis, a sensitive technique for the determination of DNA double-strand breaks.

It has been demonstrated that clamped homogeneous electrical field (CHEF) electrophoresis is a suitable method for the determination of DNA double-strand breaks in Chinese hamster ovary (CHO) cells. It allows the separation of DNA molecules up to 10 Mbp. The fraction of DNA fragments of this size is correlated with the number of radiation induced double-strand breaks. The resolution limit of the technique is equivalent to the effect of about 1 Gy (gamma-rays). Double-strand break repair was monitored after irradiation with Co-60 gamma rays and the repair time constant determined to t1/2 = 30-35 min. In combination with the detection of DNA by fluorescence, CHEF electrophoresis provides an easy and sensitive method for the determination of double-strand break repair which does not require the radioactive labelling of cells.