1. A. A. Kolykhalov, E. V. Agapov, K. J. Blight, C. M. Rice, Department of Molecular Microbiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110–1093, USA
2. K. Mihalik and S. M. Feinstone, Division of Virology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA