1. Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;
2. Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;
3. Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;
4. Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;