1. Department of Biological Sciences, School of Science; The University of Tokyo; Tokyo 113-0033 Japan
2. Department of Cell Biology; Osaka Bioscience Institute; Osaka 565-0874 Japan
3. Department of Bioscience; Nara Institute of Science and Technology; Nara 630-0192 Japan
4. Department of Chemical Physiology; The Scripps Research Institute; La Jolla California 92037
5. Laboratory of Pediatric Brain Diseases; Howard Hughes Medical Institute, The Rockefeller University; New York New York 10021-6399