1. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, United States, Department of Bacteriology, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States, Biological Institute, Section for Ecology and Evolution, University of Copenhagen, Universitetsparken 15, Building 12, 2100 Copenhagen Ø, Denmark, and Pharmaceutical Sciences Division, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States