1. Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minatoku, Tokyo 108-8639,1
2. Department of Bacteriology, Shinshu University School of Medicine, Asahi 3-1-2, Matsumoto 390-8621,2
3. Institute of Molecular and Cellular Biosciences, University of Tokyo, Bunkyoku, Tokyo 113,3 and
4. Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford California 943054
5. Department of Bacterial Toxinology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565,5 Japan, and