DNA-synthesis in synchronized L-cells after irradiation during the G1-phase of the cell cycle

Mouse fibroblast L-929 cells synchonized by mitotic selection were irradiated during the G1-phase of the cell cycle with a dose of 1000 rad. The rat of DNA synthesis was measured by 3H-thymidine incorporation, and the progression of the cells through the cell cycle was determined using a pulse-cytophotometer. Irradiation caused a decrease in the rate of DNA synthesis to half the control value, and an extension of the S-phase to twice its normal duration.