Assembly of Amsacta moorei entomopoxvirus spheroidin into spheroids following synthesis in insect cells using a baculovirus vector.

Abstract

The gene encoding the major occlusion body protein, spheroidin, of Amsacta moorei entomopoxvirus (AmEPV) was introduced into a baculovirus vector under control of the polyhedrin gene promoter. A recombinant virus produced large, ovoid occlusion body-like structures in both Spodoptera frugiperda and Trichoplusia ni cells. These structures resembled the spheroids found in AmEPV-infected Lymantria dispar cells, except they were devoid of virus particles and were not surrounded by a membrane- or envelope-like structure. These results were confirmed by immunofluoresence microscopy and Western blotting using a specific antipeptide antibody to spheroidin, and suggest that the supramolecular assembly of spheroids is not dependent on other EPV-encoded gene products. Transmission electron microscopy and subcellular fractionation experiments revealed that the spheroid-like structures were assembled in both the nucleus and cytoplasm of the recombinant virus-infected cells. This contrasts with the solely cytoplasmic localization found in AmEPV-infected cells.