1. Howard Hughes Medical Institute, Institute for Molecular Genetics, Baylor College of Medicine, Houston, TX 77030.
2. Department of Immunology, Immunex Research and Development Corporation, Seattle, WA 98101.
3. Department of Pediatrics, University of Tennessee, College of Medicine and Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN 38105.
4. Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030.
5. Mammalian Genetics Laboratory, ABL-Basic Research Program, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, MD 21702.
6. Department of Pathology, University of Washington, Seattle, WA 98195.
7. Department of Molecular Biology, Immunex Research and Development Corporation, Seattle, WA 98101.