1. Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1‐18‐1 Kamiyoga, Setagaya‐ku Tokyo 158‐8501 Japan
2. Otsuma Women's University, 12 Sanban‐chou, Chiyoda‐ku Tokyo 102‐8357 Japan
3. Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita‐12, Nishi‐6, Kita‐ku Sapporo 060‐0812 Japan
4. Istituto di Biochimica delle Proteine, Consiglio Nazionale Ricerche Via P. Castellino, 111 80131 Napoli Italy
5. Graduate School of Frontier Biosciences, Osaka University and CREST, JST, 1‐3 Yamada‐oka, Suita‐shi Osaka 565‐0871 Japan