1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, U.S.A.
2. Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, U.S.A.
3. Viral and Rickettsial Diseases Department, Infectious Disease Directorate, US Naval Medical Research Center, 8901 Wisconsin Avenue, Bethesda, MD 20889, U.S.A.