[1] Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720-1460, United States
[2] Dept. of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-1460, United States
[3] Protein and Nucleic Acid Facility, Stanford University Medical Center, Palo Alto, CA 94305, United States
[4] Department of Chemistry, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL 33620-5250, United States
[5] Dept. of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604, Tempe, AZ 85287-1604, United States
[6] Institute fur Biochemie, Martin-Luther-Univ. Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle, Germany