1. *Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892;
2. Department of Biology, Johns Hopkins University, Baltimore, MD 21218;
3. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742; and
4. Antibody Production and Purification Unit, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892