1. Department of Biochemistry and Molecular Biology, James H. Quillen College of Medicine, East Tennessee State University, Box 70581, Johnson City, TN 37614-0581, U.S.A.
2. Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, U.S.A.
3. Department of Cell Biology, The Johns Hopkins University School of Medicine, 725 N Wolfe St., Baltimore, MD 21205, U.S.A.