1. Division of Material Science, Graduate School of Science, Nagoya University, Nagoya 456-8602, Japan, Department of Biology, University College London, London, U.K., Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Shiga 525-8577, Japan, and Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka 560-0043, Japan