Polyacrylamide gel electrophoresis of the solubilized protein of rice dwarf virus (RDV), purified from RDV-infected rice plants, showed the virus to be composed of seven structural polypeptides. The molecular weights of these were calculated to be 193,000; 152,000; 131,000; 110,000; 62,000; 46,000 and 45,000 daltons.These were designated I, II, III, IV, V, VI, and VII respectively. Chymotrypsin-treatment of the virus was not effective for removing the outer components of capsid, whereas centrifugation of the virus through preformed cesium chloride gradients separated the preparation into four zones, top (T), upper-middle(M1), lower-middle (M2), and bottom (B), the buoyant densities of these being 1.26, 1.39-1.42, 1.43, and 1.46g/ml respectively. Recentrifugation of M1 through the cesium chloride gradients yielded three zones, M1, M2, and B, indicating that the latter two resulted from M1 by the shearing effect of cesium chloride centrifugation.Electron microscopy and SDSpolyacrylamide gel electrophoresis of B showed complete loss of II and IV, and a marked decrease of VI and VII, indicating that VI and VII compose the outer capsomeres and II and IV are the amorphous polypeptides that surround the outer capsomeres. The inner core was found to contain I, III, and V, among these V seemed to be the internal protein associated with nucleic acid because this was readily released from virions by freeze-thawing together with nucleic acid.
