1. Viral Evolution and Transmission Unit, DIBIT, Fondazione Centro San Raffaele, Milan, Italy.
2. HIV Databases, Theoretical Biology and Biophysics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545.
3. Division of Medical Microbiology/Virology, Department of Laboratory Medicine, Lund University, Lund, Sweden.
4. Commissariat à l'Energie Atomique, DSV/DRM, Service de Neurovirologie/Laboratoire d'Immunopathologie Expérimentale, 92265 Fontenay aux Roses, France.
5. Division of Cellular and Molecular Pharmacology, Department of Experimental Medical Science, Lund University, Lund, Sweden.
6. Department of Pediatrics, University of Milan, Clinica De Marchi, Milan, Italy.