COMPARISON OF YIELDS AND REPAIR KINETICS OF INTERPHASE CHROMOSOME BREAKS VISUALIZED BY SENDAI-VIRUS OR PEG-MEDIATED CELL-FUSION IN IRRADIATED CHO CELLS

We examined the initial yields and the kinetics of rejoining of interp hase chromosome breaks in irradiated plateau-phase Chinese hamster ova ry cells by means of premature chromosome condensation (PCC) using eit her Sendai virus or polyethylene glycol (PEG) as fusogens. We found a yield of 2.2 chromosome breaks/cell/Gy independently of the method use d to induce PCC. Rejoining of interphase chromosome breaks also procee ded with identical kinetics in cells fused using either Sendai virus o r PEG. In an additional set of experiments, we compared the kinetics o f rejoining of interphase chromosome breaks in cells synchronized in G 1 phase by elutriation to that measured in plateau-phase cells, using either Sendai virus or PEG as fusogens. Here again, the rejoining kine tics were not affected by the fusogen used, and were similar in synchr onized G1 and plateau-phase cells. These observations suggest that bot h methods of fusion give equivalent results in terms of yields and rej oining kinetics of interphase chromosome breaks. They also suggest tha t differences in the fusogens or the metabolic state of the cells cann ot explain differences in the yields, and probably also the kinetics o f the rejoining of interphase chromosome breaks that have been reporte d elsewhere. Cell line characteristics and other as of yet unidentifie d technical parameters may underlie these differences.