1. A. T. Haase, M. Zupancic, W. Cavert, K. Gebhard, K. Staskus, Z.-Q. Zhang, Department of Microbiology, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
2. G. Sedgewick, Department of Cell Biology and Neuroanatomy, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
3. R. A. Faust, Department of Otolaryngology, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
4. K. Henry and H. Melroe, HIV Program, St. Paul-Ramsey Medical Center, St. Paul, MN 55101, USA, and Department of Medicine, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
5. P. J. Dailey, Chiron Corporation, Emeryville, CA 94608, USA.
6. H. H. Balfour Jr. and A. Erice, Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
7. A. S. Perelson, Theoretical Biology and Biophysics, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.