1. Daiichi Pharmaceutical Company, Ltd., 1-16-13 Kita-Kasai, Edogawa-ku, Tokyo 134, Japan, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565, Japan, National Institute of Agrobiological Resources, 2-1-2 Kannondai, Tsukuba, Ibaraki 305, Japan, and Department of Biotechnology, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113, Japan