1. Department of Radiation Genetics; Kyoto University, Graduate School of Medicine, Yoshida Konoe; Sakyo-ku Kyoto 606-8501 Japan
2. Department of Environmental Health, School of Public Health; Seoul National University,599 Gwanak-ro; Gwanak-gu Seoul 151-742 Korea
3. Department of Mathematical and Life Sciences, Graduate School of Science; Hiroshima University, Higashi-Hiroshima; 739-8526 Japan
4. Department of Chemistry; Tokyo Metropolitan University, Minami-Osawa; Hachioji Tokyo 192-0397 Japan
5. Department of Laboratory Animal Science, School of Veterinary Science; Osaka Prefecture University, Rinku Ourai Kita; Izumisano Osaka 598-8531 Japan
6. Division of Genetics and Mutagenesis; National Institute of Health Sciences, 1-18-1 Kamiyoga; Setagaya-ku Tokyo 158-8501 Japan