Effect of cell-cycle position and dose on the kinetics of DNA double-strand breakage repair in X-irradiated Chinese hamster cells.

The kinetics of DNA double-strand breakage (d.s.b.) repair in X-irradiated Chinese hamster V79 cells were found to be affected by cell-cycle position. In mitotic cells, the repair kinetics were monophasic with a half-time value of about 32 min, whilst in G1, S, or asynchronous cultures, the kinetics were biphasic with half-time values of around 2.7 and 27 min. The repair of DNA single-strand breakage (s.s.b) was also shown to be slower in mitotic than in interphase cells. The DNA d.s.b. repair system, in both mitotic and interphase cells, showed no evidence of saturation within the X-ray dose range covered. The implications of these findings for the mechanism of DNA d.s.b. repair and for models of ionizing radiation action are discussed.