Immunocytochemical characterization of p24, a baculovirus capsid-associated protein.

An open reading frame (ORF 1) located upstream of the polyhedron envelope protein gene in the Orgyia pseudotsugata multinucleocapsid nuclear polyhedrosis virus (OpMNPV) genome was cloned in-frame into a trpE bacterial expression vector. The fusion protein produced by this construct was used for the preparation of a monospecific antiserum. Western blot analysis of extracts from OpMNPV-infected Lymantria dispar cells and Autographa californica NPV (AcMNPV)-infected Spodoptera frugiperda cells detected a 24K protein late in infection. This antiserum also reacted with a 24K protein in preparations of budded and polyhedra-derived virus from OpMNPV and AcMNPV. The 24K protein was not N-glycosylated. Immunoelectron microscopy confirmed that the OpMNPV p24 is associated with nucleocapsids of budded and polyhedra-derived virions.