Identification of the membrane protein and "core" protein of Sindbis virus

Abstract

Electron micrographs of arbovirus (insect-borne animal viruses) virions suggest that they are composed of an outer lipoprotein envelope and an inner RNA-containing core that has also been assumed to contain proteins.^(1,2) The lipoprotein envelope of the virus is apparently acquired as the core buds through an altered cellular membrane.^2 Pfefferkorn and Hunter^3 analyzed purified preparations of Sindbis virus, a group A arbovirus, and found that 28 per cent of the mass of the virion was lipid. Because several analyses of animal cell membranes have yielded protein-to-lipid ratios of 1.6-2,^(4,5)Pfefferkorn^6 reasoned that the bulk of the total protein of the virion must be in the form of lipoprotein. When it was later found that all the viral protein was synthesized de Lo after infection, the possibility was raised that the protein portion of the virus lipoprotein envelope was, in fact, specified by the virus genome. Because the RNA of this group of viruses is a molecule of about 2.0 X 10^6 daltons,^7 there was reasonable hope that their lipoprotein envelopes might be composed of only one polypeptide chain (or at most a few) combined with a specific set of lipids. The studies here reported indicate that the virion contains only two proteins-one associated with the viral RNA in a "core," the other associated with lipid to form the lipoprotein envelope of the virus.