Shope Fibroma Virus I. Biological and Molecular Properties of a Cytocidal and a Noncytocidal Strain

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The biological and molecular properties of two strains of Shope fibroma virus (SFV) were compared. SFV-I was highly cytocidal to most of the cell lines tested and produced pocks in the chorioallantoic membrane of chick embryos. By contrast, SFV-W did not produce cytopathic effects in any of the cell lines or in the chorioallantoic membrane, but it induced characteristic foci 3 to 4 days after infection. Both strains produced tumors when inoculated into the skin of susceptible rabbits. Maximal infectivity in BSC-1 cells was reached by both strains between 24 to 48 h after inoculation. Viral DNA synthesis also took place at the same time, although cells infected with SFV-I incorporated three times more [3H]thymidine than cells infected with SFV-W. Sedimentation analysis and hydroxylapatite chromatography of the two viral DNAs indicated that their molecular weights were similar and that both were naturally cross-linked. Digestion with three restriction endonucleases, however, revealed that they had different restriction sites. When SFV-I and vaccinia DNA were compared, the restriction patterns were more alike. Analysis of the virion structural proteins by gel electrophoresis indicated that SFV-I, SFV-W, and vaccinia virus had many polypeptides in common, although there were distinctive differences among the three viruses. Finally, the results of plaque neutralization tests with different antisera showed that SFV-I and SFV-W shared common antigens and that vaccinia antiserum inhibited SFV-I but not SFV-W. We conclude that the SFV-I genome contains information for both cytolysis and tumorigenesis. This unusual virus may be a recombinant between an orthopoxvirus and a leporipoxvirus.

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