1. Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, North Carolina 27599-7290
2. Department of Microbiology and Immunology, Health Sciences Center, West Virginia University, Morgantown, West Virginia 26506-9177
3. UMDNJ-Robert Wood Johnson Medical School and Howard Hughes Medical Institute, Piscataway, New Jersey 08854-5627
4. Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019-0370