Studies on the mechanism of entry of vaccinia virus in animal cells

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Abstract
In order to study the mechanism of entry of vaccinia virus into cells the fate of virion associated polypeptides was investigated during infection of african green monkey kidney (BSC-40) cells with 35 S-methionine labelled virus. Approximately 12–15 percent of the virion polypeptides were degraded to acid-soluble products by 3 hours post-infection. Proteolysis was inhibited (50 percent) by methylamine, suggesting a lysosomal site of degradation. Neither methylamine or chloroquine inhibited virus infectivity or uncoating indicating a non-acid endocytic mechanism of entry. Subcellular fractionation studies on density gradients indicated that the bulk of the input virion polypeptides were associated with the plasma membrane fraction. In addition, input virion DNA was partially resolved from the membrane fraction. The results are most consistent with a mechanism of entry involving fusion of the virus with the plasma membrane.