Studies on the substructure of togaviruses

Summary

The viruses of equine arteritis, rubella, bovine viral diarrhea and hog cholera have been concentrated and purified. In preparations negatively stained with uranyl acetate they appeared as roughly spherical particles about 60 nm across. Within their envelopes isometrical cores were detected after spontaneous disruption or upon pretreatment; they are considered to be the viral nucleocapsids. The lower coefficients of variation calculated for the nucleocapsids as compared with those of the respective virus particles indicate that the pronounced heterogeneity in virion size must be attributed to the envelope. Ringlike morphological subunits observed on the surface of the spherical nucleocapsids and the presence of centra] core components suggest that the four viruses should be classified as togaviruses (lipid-containing RNA viruses with cubic symmetry of the nucleocapsid), together with arbo-A-viruses. The bovine viral diarrhea and hog cholera viruses differ from the other viruses studied in their lower sedimentation and density values, their lesser nucleocapsid diameters and an unusual “rosary” envelope structure. A further subdivision of the togavirus group is discussed.