1. C. K. Lapham and H. Golding, Division of Viral Products, Center for Biologics Evaluation and Research (CBER), Food and Drug Administration, Building 29B, Room 3G21, HFM 454, 8800 Rockville Pike, Bethesda, MD 20892, USA.
2. J. Ouyang and D. S. Dimitrov, Section on Membrane Structure and Function, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
3. B. Chandrasekhar and N. Y. Nguyen, Facility for Biotechnology Resources, CBER, Food and Drug Administration, Bethesda, MD 20892, USA.