1. Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, DHHS, Bethesda, Maryland 20892-4256, Department of Molecular Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan, Laboratory of Experimental Carcinogenesis, National Cancer Institute, NIH, Bethesda, Maryland, BD Biosciences Pharmingen, San Diego, California 92121, and Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary