Properties and amino acid composition of polyoma virus purified by zonal ultracentrifugation

Virion and capsid preparations of three different strains of polyoma virus have been purified by the use of the Anderson zonal ultracentrifuge. This technique permits good recovery of the infectivity of large volumes of virus-infected mouse kidney cell lysates and yields polyoma virion and capsid preparations with a high degree of purity, as determined by equilibrium density-gradient centrifugation, band- and boundary-centrifugations, and by chemical composition analysis. Briefly, the procedure consists of the concentration of the virus particles by ammonium sulfate precipitation (50% saturation), extraction of the particles from the precipitate with 0.5% sodium deoxycholate, 0.02 m Tris-HCl (pH 9.0) and the fractionation of the virions and capsids by centrifugation in the zonal ultracentrifuge. The amino acid compositions of purified virion and capsid preparations representing three strains of virus have been determined. The virion preparations have a higher content of lysine, arginine and alanine and a lower content of aspartate, methionine and leucine, when compared to capsids of the same strain. It is suggested that the virions contain a basic polypeptide in addition to the structural capsid protein present in both virions and capsids. The amino acid compositions of the two large-plaque strains have been found to be similar. The small-plaque strain contains more lysine and serine residues and less methionine, when compared to either of the large-plaque strains. The immunologic reactivities of the three strains, determined by complement fixation, are in agreement with the amino acid analyses. The two large-plaque strains are antigenically identical; the small-plaque particles are significantly different from the large-plaque particles.