Study of the Papilloma Virus Protein with the Electron Microscope. ∗

Abstract

Information relative to the physical character of the papilloma virus protein 1 has been obtained by means of ultracentrifugation, 2 electrophoresis, 3 , 4 diffusion and viscosity. 2 Recently, more direct studies of this animal virus have been undertaken with the electron microscope. In the present paper are described the preliminary observations dealing chiefly with data gathered with this instrument relative to the appearance and size of the virus.

Papilloma virus protein isolated in 0.05 M phosphate buffer pH 6.5 by previously described ultracentrifugal procedures was diluted with water to concentrations of the order of 0.05 to 0.5 mg per cc. The salt concentration in the final solutions was approximately 0.005 M. Preparations for study were made by pipetting the solutions onto collodion membranes supported on 200-mesh wire gauze. Free fluid was removed with the pipette, and the resulting thin film allowed to dry in the air. For comparison, examinations have been made also of mixtures of papilloma and tobacco mosaic viruses† the latter in concentration of about 0.4 mg per cc of the mixture.

The essential findings are illustrated in Figs. 1 and 2. In Fig. 1 are shown the results obtained with papilloma virus alone. Repeated micrographs of 3 different batches of the purified protein have resulted consistently in observation of the circular images shown in Fig. 1. When the protein concentration was kept in the region of approximately 0.1 mg per cc, the images were for the most part single, though grouping was frequent as seen in Fig. 1. In preparations of higher concentration, large groups of particles occurred and fewer single images were seen. A regular arrangement of images in the groups was not observed.