VP19 was identified as an envelope protein. (A) Western blotting revealed that VP19 could only be detected in the envelope fraction. Purified SGIV viral particles were incubated with PBS (pH 7.4), PBS with 1% Triton X-100, or PBS with 0.1% SDS separately as described in methods. After centrifugation, the supernatant (S) and pellet (P) fractions were electrophoresed by SDS-PAGE. Western blotting was performed using anti-VP19 or anti-MCP serum. (B) Ultrastructure of purified intact virus particles (virion) and viral nucleocapsids was determined under scan electron microscopy (SEM). (C) Ultrastructural localization of VP19 in virus particles. The localization of VP19 and MCP were detected after incubation with immunogold-labeled anti-VP19 and anti-MCP antibodies. The anti-VP19 antibody bound on virions, but not viral nucleocapsids, while the anti-MCP antibody bound on viral nucleocapsids, but not virions.