Purification of Encephalomyocarditis Virus

Virus Research Unit, Medical Research Council Laboratories, Carshalton, Surrey By combining the techniques of acid precipitation, organic solvent extraction, enzyme treatment and differential centrifugation, concentration of encephalomyocarditis virus more than 1000-fold with 30% to 50% yield and a degree of purification of more than 1 x 10 4 was achieved. Yield was estimated by adding virus labelled with 32 P to crude virus and measuring the percentage recovery both of the radioactive label and of the total number of plaque forming units in the final product. The degree of purification was determined by adding both 32 P-and 3 H-labelled, uninfected host-cell material to crude virus and measuring the extent to which the final product was contaminated with radioactive label. Pure virus comprised a homogeneous preparation of polyhedral particles with a particle to plaque forming units ratio of 250 ± 40 and gave a single, symmetrical peak in the analytical ultracentrifuge. * Present address: Sloan-Kettering Institute for Cancer Research, New York, New York 10021, U.S.A. Received 17 December 1968; accepted 14 April 1969.