1. Chemical Biology Laboratory, National Cancer Institute, Frederick, Maryland 21702, United States
2. Protein Characterization Laboratory, Frederick National Laboratory for Cancer Research, Frederick, Maryland 21701, United States
3. Laboratoire de Biologie Moléculaire Eucaryote, Toulouse 31062, France
4. Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
5. Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, Bethesda, Maryland 20892, United States