From the *Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany; the ‡Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892; and the §Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892 (1997-04-07時点)