Density Gradient Centrifugation Studies on Rubella Complement-Fixing Antigens

Abstract

Summary Rubella virus preparations consisting of concentrated fluids from infected BHK -21 cultures and alkaline buffer extracts of infected cells were subjected to equilibrium centrifugation in sucrose, Ficoll and cesium chloride density gradients. In sucrose gradients two distinct complement-fixing (CF) moieties were demonstrated, one at densities of 1.23 to 1.19 g/ml, and the other at densities of 1.14 to 1.08 g/ml. The more dense antigen was shown to correspond to large particle antigen, and the lighter to small-particle (“soluble”) antigen, which are separable by Sephadex gel filtration. Infectivity was generally found in the region of the dense, large-particle CF antigen, although in some experiments it showed a wider range of densities. Treatment of large- and small-particle antigens with ether did not markedly alter their densities, suggesting that lipids are not an integral part of either CF antigen. Ficoll gradients could be used to separate large-particle CF antigen and infectious virus from the light, small particle CF antigen, but the densities obtained in these gradients were too low to permit the large-particle CF antigen and infectious moiety to equilibrate in the gradient; instead they were recovered in the pellet. In CsCl gradients both CF antigens and infectious virus showed higher apparent buoyant densities than those obtained in sucrose or Ficoll gradients, possibly due to interaction of the cesium with the viral components.