1. Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
2. Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755, USA;
3. Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA
4. Cornell University, Ithaca, New York 14853, USA