1. Departments of Medicine and Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294.
2. Department of Medicine, Duke University, Durham, North Carolina 27710.
3. Institute of Genetics, University of Nottingham, Queens Medical Centre, Nottingham NG7 2UH, England.
4. IMEA-INSERM U552, Hôpital Bichat-Claude Bernard, 75018 Paris, France.
5. Laboratoire Retrovirus, UMR036, IRD, University of Montpellier I, 34032 Montpellier, France.
6. Howard Hughes Medical Institute, University of Alabama at Birmingham, Birmingham, Alabama 35294.