Induction and Repair of DNA Strand Breaks in CHO-cells Irradiated in Various Phases of the Cycle

Summary

Induction and repair of DNA strand breaks was investigated in synchronized CHO cells by using the alkaline DNA-unwinding technique followed by chromatography on hydroxyapatite. The velocity of DNA denaturation in an alkaline solution (pH 12·1) was found to be independent of the position in the cycle. In unirradiated cells the number of DNA strand breaks per 3·6 × 10¹² dalton was found to vary with age in cell cycle amounting to about 250 breaks per cell for G₁, 400 for S, and 500 for G₂ + M cells. The number of induced DNA strand breaks per unit dose was found to be the same in all phases; an average of 340 strand breaks were induced per Gy and per 3·6 × 10¹² dalton. Within the first hour after irradiation about 90 per cent of all radiation-induced strand breaks are rejoined.