1. Department of Microbiology; The Jikei University School of Medicine; Minato-ku Tokyo 105 Japan
2. Department of Molecular Biology; Nagoya City University School of Medicine; Nagoya Aichi 467 Japan
3. Division of Morphology, The Institute of Medical Science; The Jikei University School of Medicine; Minato-ku Tokyo 105 Japan
4. Department of Microbiology; Fukuoka University School of Medicine; Fukuoka Fukuoka 814-01 Japan
5. Nissin Molecular Biology Institute; Boston MA 02215 U.S.A.