The Production of Strand Breaks in Mammalian DNA by X-Rays: At Different Stages in the Cell Cycle

The formation of strand breaks induced by x-rays in the DNA of Chinese hamster ovary cells has been studied as a function of the position of the cells in the cycle by alkaline EDTA-sucrose sedimentation. The efficiency of total strand breakage was found to be the same throughout the cell cycle and equal to 60 ± 10 eV per break. This figure was obtained from the best fit of a random distribution to the observed size distribution at high x-ray doses; by computation from a direct evaluation of the number-average molecular weight at low doses; and also at low x-ray doses from the destruction of the monodisperse distributions associated with the structural chromosomal subunits.