Cell cycle dependence for the induction of 6-thioguanine-resistant mutations: G2/M stage is distinctively sensitive to 252Cf neutrons but not to 60Co gamma-rays.

Cell cycle dependence for the induction of 6-thioguanine-resistant mutation was investigated using synchronized mouse L5178Y cells after exposure to 4 Gy to 60Co gamma-rays or 1 Gy of 252Cf radiation (fission neutrons). Maximal mutation frequency was observed immediately after release from colcemid block (G2/M phase) after 252Cf radiation, whereas it was 1 h after the release (G1 phase) after 60Co gamma-rays. When the mutation frequency was plotted against the surviving fraction, a general correlation was observed between the two parameters except for G2/M and G1 phases which were more mutable per lethal event for 252Cf and 60Co radiations, respectively.