1. T. Todo, T. Inui, H. Ayaki, M. Ikenaga, Radiation Biology Center, Kyoto University, Yoshida-konoecho, Sakyo-ku, Kyoto 606-01, Japan.
2. H. Ryo and T. Nomura, Department of Radiation Biology, Faculty of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565, Japan.
3. K. Yamamoto, Department of Biology, Faculty of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-77, Japan.
4. H. Toh, Department of Biochemical Engineering and Science, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka 820, Japan.