Effect of Oxygen on DNA Strand Breaks in Irradiated Thymocytes

Abstract

Single and double-strand breaks were determined in DNA of rat thymocytes irradiated with 10-MeV electrons over a range of 0 to 6 Mrads in the presence of O/sub 2/ or N/sub 2/, under rapid conditions where the repair of breaks should have been negligible. The numbers of double and single strand breaks in irradiated cells increased linearly with dose. The ratio between single and double strand breaks was 19.5 plus or minus 1.3 in DNA from cells irradiated under O/sub 2/ and N/sub 2/. DNA from irradiated cells contained fewer singlestrand breaks after heating than after alkaline denaturation. The frequency of single strand breaks in unirradiated DNA was identical after both methods of denaturation. The ratio of the slopes of the dose-effect curves yielded 27.8% plus or minus 3.8% alkali labile breaks under O/sub 2/ and 49.8 plus or minus 4.7% under N/sub 2/. An o.e.r. of ~3.7 was deduced from these results for the initial yield of single- and doublestrand breaks in irradiated mammalian cells. (UK)