PROTEIN COMPOSITION OF POLYOMA VIRUS

The protein coat of polyoma virus can be dissociated into subunits of uniform molecular size by treatment with sodium dodecyl sulfate and mercaptoethanol at elevated temperature and pH. The subunit preparations show one band migrating toward the anode on acrylamide gel electrophoresis at pH 9.0, and a single peak by sucrose gradient centrifugation. A single precipitin arc is obtained when subunit preparations react with rabbit antiserum by double diffusion in agar. The diffusion constant of the protein has been estimated to be 6.6 × 10-6 cm2 sec-1 when measured by immunodiffusion. An estimated molecular weight of 50,200 was obtained for the subunit protein by equilibrium sedimentation determinations. This value agrees well with the value of 46,000 which was calculated for the molecular weight of the subunits from chemical composition data and the assumption that the virus capsid is composed of identical protein subunits arranged according to the Caspar-Klug theory of virus structure. Acrylamide gel electrophoresis at acid pH has provided evidence that the polyoma virions contain an internal basic polypeptide, comprising about 10% of the total virus protein. Capsid preparations do not contain this component. © 1968.