CELL-CYCLE-DEPENDENT RADIATION-INDUCED ONCOGENIC TRANSFORMATION OF C3H 10T1/2 CELLS

C3H 10T 1/2 cells were synchronized by a modified mitotic shake-off procedure. X irradiation of cells at various intervals after mitotic harvest indicated a single narrow window (about 2 h) of sensitivity to the induction of oncogenic transformation. It is not possible to delineate precisely the time in the cycle at which this sensitivity is expressed. The most likely candidate is G2 phase, though we cannot eliminate the possibility that the sensitive period begins in late S phase. In the same synchronized cells, cell lethality showed the conventional pattern, i.e., sensitivity in mitosis and resistance in late S and in G1 phase.