1. Department of Microbiology and Immunology, Weill Cornell Medical College, New York, New York.
2. Department of Medical Microbiology, Academic Medical Center, 1105 AZ Amsterdam, The Netherlands.
3. Ragon Institute of MGH, MIT, and Harvard, Massachussetts General Hospital and Division of AIDS, Harvard Medical School, Boston, Massachusetts.
4. Department of Biochemistry, Weill Cornell Medical College, New York, New York.
5. Howard Hughes Medical Institute, Massachusetts General Hospital and Division of AIDS, Harvard Medical School, Boston, Massachusetts.