Comparative study of the repair kinetics of chromosomal aberrations and DNA strand breaks in proliferating and quiescent

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Abstract
Repair kinetics observable at the level of exchangetype chromosomal aberrations (dicentric chromosomes), using fractionation and delayed-plating techniques, have been compared with repair kinetics of radiation-induced DNA double-strand breaks, measured with PFGE, and with repair kinetics of all strand breaks, measured with the alkaliunwinding technique. Only data from quiescent or proliferating CHO K1 cells obtained in the same laboratory were used. We determined repair kinetics in terms of the time constant tau (equal to half-time/log e2). The repair kinetics (tau 11-14 min) observed in the split-dose formation of dicentric chromosomes agrees with fast repair kinetics of double-strand breaks (tau 11-13 min), thus permitting us to identify the latter as the 'primary lesions' whose pairwise interaction leads to the beta D 2 yield term of the aberrations. The repair kinetics observed for dicentric chromosomes formed under delayed-plating conditions (tau 75 min), which mainly affects the alpha D yield term, is attributed to an intermediate interchromosomal product temporarily existing in the course of aberration formation; it is suggested that this product is mechanistically correlated with the slow repair kinetics of 'clustered damage' to DNA seen with the applied molecular methods (tau 90 min).
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