1. From the Departments of Biochemistry and Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai; The Institute of Public Health, Ministry of Health and Welfare, Tokyo; Departments of Hematology and Oncology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima; Center for TARA and Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Japan.