1. Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 373-1, Kusung-dong Yusung-gu, Taejon 305-701, Korea, School of Chemical Engineering, Yeungnam University, Dae-Dong, Kyungsan 712-749, Korea, Institut für Biochemie, Universität zu Köln, Zülpicher Strasse 47, 50674 Köln, Germany, and Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, Connecticut 06520-8114