1. Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
2. Molecular Embryology Group, Advanced Biosciences Laboratory-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, MD 21701.
3. Eukaryotic Signal Transduction Group, Advanced Biosciences Laboratory-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, MD 21701.