1. Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan
2. Division of Biology, Department of Biological Sciences, School of Science, Hokkaido University, Sapporo 060-0810, Japan
3. Present: Department of Genome Sciences, University of Washington, Seattle, WA, USA
4. Present: Bioorganic Research Institute, Suntory Foundation for Life Sciences, Kyoto 619-0284, Japan
5. Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan