1. Department of Biology, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
2. Department of Microbiology and Immunology, Graduate School of Medicine, Hokkaido University, Kita-ku, Sapporo 060-8638, Japan.
3. Department of Virology, Faculty of Medicine, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan.
4. Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.