1. Department
of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114,
United States
2. School of
Life Sciences, Steitz
Center for Structural Biology, Gwangju Institute of Science and Technology (SCSB-GIST), 261 Cheomdan-gwagiro, Buk-gu,
Gwangju 500-712, Republic of Korea.