1. Contribution from the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1, Komaba, Meguro-ku, Tokyo 153-8902, Japan, Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Biomolecular Engineering Research Institute, 6-2-3, Furuedai, Suita, Osaka 565-0874, Japan, and National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan