1. Molecular Targets Program, Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702-1201, United States
2. Basic Science Program, Frederick National Laboratory for Cancer Research sponsored by the National Cancer Institute, Frederick, Maryland 21702-1201, United States
3. Genetics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, United States
4. Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, United States
5. Department of Analytical Research and Development, MRL, Merck & Co., Inc., Rahway, New Jersey 07065, United States