1. Molecular Medicine Laboratories, Institute for Drug Discovery Research, Yamanouchi Pharmaceutical, Tsukuba, Ibaraki 305-8585,1
2. Institute for Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, 2 and
3. Institut de Genetique et de Biologie Moleculaire et Cellulaire, (IGBMC)/CNRS/INSERM/ULP College de France, 67404 Illkirch Cedex, C.U. de Strasbourg, France3
4. CREST, Japan Science and Technology, Kawaguchi, Saitama 332-0012, 4 Japan, and