1. Department of Biochemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
2. Department of Chemistry and Howard Hughes Medical Institute, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
3. Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States