1. Division of Immunology, Institute for Molecular and Cellular Biology, Osaka University, 1-3, Yamada-Oka, Suita, Osaka 565, Japan.
2. Department of Molecular Biology, Masssachusetts General Hospital, Boston, MA 02114.
3. Division of Molecular Biology, Institute for Molecular and Cellular Biology, Osaka University, 1-3, Yamada-Oka, Suita, Osaka 565, Japan.