Abstract
Groupe de Recherches de l'I.N.S.E.R.M. (U 74) sur la Pathogénie des Infections Virales et Laboratoire de Virologie de la Faculté de Médecine, Université Louis Pasteur, 3, rue Koeberlé, 67000 Strasbourg, France
Enveloped and naked frog virus 3 particles have been separated on sucrose gradients and their morphology checked by electron microscopy. Naked nucleocapsids sedimented at a density of 1.25 g/ml and enveloped virions at a density of 1.20 g/ml. The enveloped virions were found to possess an additional 58 K mol. wt. polypeptide. The ratio between the number of infectious particles, determined by plaque titration, and that of physical particles established by radioactive labelling as well as by electron microscopic counts, showed that the infectivity of the enveloped particles could be up to 150-fold greater than that of naked ones.