Studies on the substructure of togaviruses

Summary

When purified Sindbis virus was incubated with 6.4m urea and examined electron microscopically its nucleocapsid could be demonstrated within the envelope after negative staining using uranyl acetate. Treatment resulted in an increase in thickness of the viral membrane (70–100 Å) that sometimes displayed a triple-layered structure.-The effect of deoxycholate appeared to be a successive degradation of at least two layers of the envelope; intact nucleocapsid particles were encountered in preparations treated with the detergent at a concentration of 0.1 per cent. Saponin (>0.01 per cent) acted on the viral membrane by disintegration and formation of masses of loops and coils. The effect on the viral surface was reflected by a substantial rise in hemagglutinating activity of the preparation, which was accompanied by a decrease in infectivity. After fixation of saponin-treated virus preparations with osmium tetroxide vapor, intact nucleocapsid particles could be demonstrated. The methods of pretreatment presented may prove useful for the demonstration of nucleocapsids in enveloped viruses and especially for the identification of togaviruses.