Proteins are cointernalized with virion particles during early infection.

Mammalian cells infected with enveloped or naked animal viruses become permeabilized to several proteins. The entry of alpha-sarcin, horseradish peroxidase, and luciferase is greatly increased during the early stages of viral infection. This process is promoted by uv-inactivated SFV, but not by heat-inactivated virions, suggesting that the process does not require viral gene expression. The entry of alpha-sarcin has been monitored both by its effects on protein synthesis and by indirect immunofluorescence. Increased entry of alpha-sarcin and luciferase is clearly observed in animal virus-infected cells by fluorescence microscopy. Chloroquine blocks the coentry of alpha-sarcin with enveloped, but not with naked, viruses. These results have implications to elucidate the mechanisms involved in virus entry.