1. Departments of Biochemistry and Molecular Biophysics (G.K.W., H.T.L.D., T.B., G.H., C.E.D., M.R.H.), College of Medicine, University of Arizona, Tucson, Arizona 85724;
2. Microbiology and Immunology (S.F.S., R.M.B., J.J.M.), College of Medicine, University of Arizona, Tucson, Arizona 85724;
3. Department of Zoology and the Division of Life Sciences (L.A.M., J.H.Y.), University of Toronto at Scarborough, Ontario, Canada M1C 1A4