1. Department of Biological Sciences; Graduate School of Science; The University of Tokyo; Bunkyo-ku Tokyo 113-0033 Japan
2. Molecular Membrane Biology Laboratory; RIKEN Advanced Science Institute; Wako Saitama 351-0198 Japan
3. PRESTO; Japan Science and Technology Agency; 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan