1. Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, Virginia 22908
2. Torrey Mesa Research Institute, San Diego, California 92121
3. Department of Immunology, Baylor College of Medicine, Houston, Texas 77030
4. Howard Hughes Medical Institute and the Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
5. Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037