Purification of viruses by centrifugation in gradients of inert substances.

By using a reorienting gradient centrifuge rotor cut from a block of Nylon and fitted with eight septae, it was possible to separate the components of the haemolymph of the mollusc Turbo sarmaticus into three fractions in a sucrose gradient held in the bowl of the rotor. The fractions were (108 and 98)S, 44S and 16-22S. The success of the experiment was due to the large differences in the sedimentation coefficients of the components. When the rotor was applied to the natural mixture of the five viruses of the caterpillars of Nudaurelia cytheria only the main component could be isolated in a pure state. The viruses were separated by isopycnic centrifugation in "self formed" caesium chloride gradients, using a Beckman Model E analytical centrifuge in which a separation cell fitted with a centerpiece with two perforated partitions was used.