1. Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
2. Protein Expression Laboratory, SAIC-Frederick, Inc., National Cancer Institute at Frederick, Frederick, Maryland 21702, United States
3. Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, United States