Purification and electron microscopy of tomato spotted-wilt virus

Tomato spotted-wilt virus is reversibly aggregated by 0.1 M potassium phosphate. It was partly purified by grinding diseased plants with 0.1 M, pH 7 potassium phosphate buffer, centrifuging the extract at low speed and resuspending the pellet in 0.01 M Na 2SO 3, in which the virus was dispersed. Ordinarily this virus solution was given one cycle of differential centrifugation and density-gradient centrifugation. It was important to use source plants at a stage of the disease in which they contained a peak concentration of virus. Examinations of the virus by electron microscopy indicated that the size of the particle is about 85 mμ across. The considerable variation in particle shape noted in certain preparations may be related to the instability of the virus. The infective particles sedimented at the same rate in density-gradient centrifugation as did the particles observed in the electron microscope. The virus sedimented in density-gradient columns at a rate expected for a particle with a sedimentation constant three times that of tobacco mosaic virus and a density of 1.21 g/cc.