1. Division of Infectious Diseases, Massachusetts General Hospital, Cambridge, Massachusetts 02139
2. Department of Biology, City College and Graduate Center of the City University of New York, New York, New York 10031
3. Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115
4. Radioisotope Center
5. Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, Shizuoka, Japan