1. Department of Applied Biological Chemistry, The University of Tokyo, Bunkyo-Ku, Tokyo 113, Japan, The Institute of Physical and Chemical Research (RIKEN), Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan, and Nara Institute of Science and Technology (NAIST), Takayama 8916-5, Ikoma-shi, Nara 630-01, Japan