Kinetics of Chromosome Lesion Repair in Synchronized Quiescent and Proliferating CHO Cells

Summary

The induction of chromosome aberrations by X-rays was investigated in synchronized quiescent and proliferating CHO-K1 cells. Kinetics of chromosome lesion repair was studied using the method of fractionated irradiation. In both cell types the time-course of repair during fractionation intervals followed first-order kinetics. Comparison with kinetic data reported on DNA double-strand break repair supports the hypothesis that DNA double-strand breaks are the lesions underlying chromosome aberration formation. Quiescent CHO cells showed higher aberration yields than proliferating cells, and chromosome lesion repair was faster in quiescent cells. This correlation can be interpreted in terms of a higher degree of repair synchronism during pairwise lesion interaction. The effect of delayed plating on aberration induction was studied in quiescent cells. The time-course of repair active during the delayed plating interval followed first-order kinetics. The kinetics observed in delayed plating experiments is slower than the repair kinetics observed in fractionation experiments, suggesting the involvement of two different processes.