1. Department of Molecular Genetics; School of Dentistry and Dental Research Institute; Seoul National University; Seoul 110-749 Korea
2. Department of Cell and Developmental Biology; School of Dentistry and Dental Research Institute; Seoul National University; Seoul 110-749 Korea
3. Department of Molecular Cell Science; Molecular Enzymology; Graduate School of Agricultural Science; Tohoku University; Miyagi 981-8555 Japan