1. Department of Chemistry, St. Olaf College, Northfield, Minnesota 55057
2. Department of Genetics, Cell Biology and Development
3. Laboratories of Genetics and Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706
4. Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
5. Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455