1. From the Department of Molecular Behavioral Biology, Osaka Bioscience Institute, Furuedai, Suita, Osaka 565, Japan; PRESTO, Japan Science and Technology Corporation, Furuedai, Suita, Osaka 565, Japan; R&D Division, Pharmaceuticals Group, Nippon Kayaku Co., Ltd. Shimo, Kita-ku, Tokyo 115, Japan; and the Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka Universi