1. Laboratory of Molecular Genetics, Tsukuba life Science Center, Institute of Physical and Chemical Research (RIKEN) Tsukuba, lbaraki 305, Japan
2. Department of Pharmaceutical Sciences, Science University of Tokyo Tokyo, Shinjuku-ku, Tokyo 162, Japan
3. Molecular Oncology Laboratory, Nippon Veterinary and Zootechnical College College, Taito-ku, Tokyo 110, Japan