Our data also raise a possibility that RET/PTC rearrangement can be initiated by a complex DSB that is induced in one of the fusion partner genes..     ///    "IR causes double-strand breaks (DSBs), suggesting that such damage leads to RET/PTC, but the rearrangement mechanism has not been established. "    ///    "Although all but one RE caused DSB in one or more of the three genes involved in RET/PTC, rearrangement was detected only in cells electroporated with either PvuII (25 and 100? U) or StuI (100 and 250 ?U). "    ///    "Chromosomal rearrangements, such as RET/PTC, are characteristic features of radiation-associated thyroid cancer and can be induced by radiation in vitro. "    ///    Both enzymes that produced RET/PTC had restriction sites only in one of the two fusion partner genes.     ///    "Moreover, the two enzymes that produced RET/PTC had restriction sites present in clusters, which was not the case for RE that failed to induce RET/PTC. "    ///    "To study the mechanism, we explored the possibility of inducing RET/PTC by electroporation of restriction endonucleases (REs) into HTori-3 human thyroid cells. "