1. Department of Microbiology, University of Washington School of Medicine, Campus Box 357242, 1959 N.E. Pacific St., Seattle, Washington 98195
2. Department of Genome Sciences, University of Washington School of Medicine, Campus Box 355065, 1705 N.E. Pacific St., Seattle, Washington 98195
3. Department of Medicine, University of Washington School of Medicine, Harborview Medical Center, Campus Box 359640, 325 9th Avenue, Seattle, Washington 98104
4. Department of Pharmacology, Program in Biomolecular Structure, Campus Box 8303, University of Colorado—Denver School of Medicine, Aurora, Colorado 80045