1. Department of Molecular Virology, Research Institute for Microbial Diseases
2. Department of Genetics, Graduate School of Medicine, Osaka University, Osaka 565-0871
3. Department of Gastroenterology, Graduate School of Medicine, University of Tokyo, Tokyo 113-8655
4. Department of Microbiology, Faculty of Medicine, Yamanashi University, Yamanashi 409-3898, Japan