1. From the Departments of Internal Medicine (B.M.S., S.J., B.S., W.H.T., F.J.M.), Microbiology (J.C.D.H.), Anatomy and Cell Biology (J.S.), Biochemistry (L.G.), and Protein Crystallography Facility (L.G.), University of Iowa, Iowa City; and Veterans Affair Medical Center, Iowa City, IA (F.J.M.).