1. Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843
2. Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104
3. Department of Chemistry, Texas A&M University, College Station, Texas 77843
4. Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas 77843
5. Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003.