Application of pulsed field gel electrophoresis to determine gamma-ray-induced double-strand breaks in yeast chromosomal molecules.

The frequency of DNA double-strand breaks (dsb) was determined in yeast cells exposed to gamma-rays under anoxic conditions. Genomic DNA of treated cells was separated by pulsed field gel electrophoresis, and two different approaches for the evaluation of the gels were employed: (1) The DNA mass distribution profile obtained by electrophoresis was compared to computed profiles, and the number of DSB per unit length was then derived in terms of a fitting procedure; (2) hybridization of selected chromosomes was performed, and a comparison of the hybridization signals in treated and untreated samples was then used to derive the frequency of dsb. The two assays gave similar results for the frequency of dsb ((1.07 +/- 0.06) x 10(-9) Gy-1 bp-1 and (0.93 +/- 0.09) x 10(-9) Gy-1 bp-1, respectively). The dsb frequency was found to be linearly dependent on dose.