1. M. Amano, K. Chihara, Y. Fukata, N. Nakamura, K. Kaibuchi, Division of Signal Transduction, Nara Institute of Science and Technology, Ikoma 630-01, Japan.
2. K. Kimura, Division of Signal Transduction, Nara Institute of Science and Technology, Ikoma 630-01, Japan, and Second Department of Anatomy, Kyoto University Faculty of Medicine, Kyoto 606, Japan.
3. Y. Matsuura, Department of Virology II, National Institute of Health, Tokyo 162, Japan.