1. Department of Pathology and Immunology
2. Department of Exploratory Medicinal Sciences, Central Research, Pfizer, Inc., Groton, Connecticut 06340
3. Eppley Institute for Research in Cancer and Allied Diseases, Department of Biochemistry and Molecular Biology, Omaha, Nebraska 68198
4. Department of Pathology and Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110
5. Institute for Molecular Biology and Biotechnology, Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
6. Regulation of Cell Growth Laboratory, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702