A Quantitative Comparison of Potentially Lethal Damage Repair and the Rejoining of Interphase Chromosome Breaks in Low Passage Normal Human Fibroblasts

After long postirradiation incubation periods, the residual frequency of prematurely condensed chromosome fragments following X-ray exposure of noncycling diploid human fibroblasts was found to be correlated with the frequency of chromosome aberrations observed under identical treatment conditions when the cells were subcultured and scored after they reached mitosis. Over a wide range of doses, the proportion of such cells without aberrations at their first metaphase was not significantly different from the proportion able to form macroscopic colonies. Further, the rate of rejoining of interphase chromosome breaks was the same as the rate of increase in survival due to the repair of potentially lethal damage (PLD). These results suggest that there is a one-to-one correspondence between the initial breakage and rejoining of G0 chromosomes and the induction and repair of PLD measured by delayed plating from plateau-phase cultures of these cells.