1. Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
2. Present address: University of Pittsburgh School of Medicine-MSTP, Pittsburgh, PA 15261.
3. Laboratory of Host Defense, RIKEN Research Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan.
4. Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan.