The purification of four strains of poxvirus

Abstract

A method is described for the purification of four strains of poxvirus belonging to the vaccinia-variola subgroup. The source of virus is the chorioallantoic membrane of infected developing chick embryos. The recovery of virus ranges from 33 to 62%. In the case of one particular virus strain, over one-third of a milligram of virus per infected membrane can be isolated. The purified virus suspensions are homogeneous in density gradients and contain no material reacting serologically as host tissue. Electron micrographs show that very little material not identifiable as virus particles is present. The suspensions contain no hemagglutinin and are devoid of alkaline phosphatase activity. Particle counts by means of the electron microscope have been related to protein mass and optical density at 260 mμ. Measurement of the latter provides rapid and accurate estimate of the number of elementary bodies. Data are presented on the efficiency of plating of the four virus strains. The four virus strains are indistinguishable in their DNA content and its base composition. All contain between 50 and 60 μg DNA per milligram of protein. The molar ratios of adenine to thymine, and of guanine to cytosine are close to 1. The molar dissymmetry ratio ( A + T G + C ) is close to 1.70.