SV40 DNA amplification and reintegration in surviving hamster cells after 60Co gamma-irradiation

SV40-transformed Chinese hamster embryo cells were exposed to 60Co gamma-irradiation and the fate of the integrated SV40 sequences was pursued over a period of 20 days following radiation exposure. As shown by colony hybridization, integrated SV40 sequences were amplified in surviving and non-surviving cells. At later times, however, clonal sublines of surviving cells grown for 20-30 cell generations after irradiation had lost most of their amplified SV40 copies but showed altered restriction fragment patterns indicating reintegration of SV40 sequences at new sites of the hamster genome. This suggests that 60Co gamma-irradiation can generate mutations by inducing over-replication of chromosome segments that are then substrates of enzymatic rearrangements.