Abstract
Shope papilloma virus from warts of cottontail rabbits was partially purified by differential centrifugation and then subjected to rate zonal centrifugation in sucrose or glycerol density gradients where the particles were separated into three bands and a small pellet. The top component consisted of particles that were of characteristic size for papilloma virus but, upon examination in the electron microscope, after treatment with phosphotungstic acid, most of them appeared to be hollow. This fraction also gave a protein-like absorption curve in the ultraviolet, contained very little phosphorus, and was almost noninfectious. By contrast the particles in the middle band appeared completely formed, contained appreciable phosphorus, had a nucleoprotein-like absorption curve, and were highly infectious. It is not known whether the two types of particle are produced as such in the host or are a result of preparation. In all particles a pattern of spots was seen either over the surface or around the periphery. The spots were of uniform size and were arrayed in a definite pattern, suggesting that they represent a subunit structure.
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