1. Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110.
2. Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110.
3. Departments of Pathology, and Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110.
4. Department of Clinical Chemistry, University of Göteborg, Sahlgren's Hospital, S-413 45 Goteborg, Sweden.