1. Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
2. Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD20892, USA.
3. Biotechnology Unit, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.