Identification and immunocharacterization of a 25K structural protein in Autographa californica nuclear polyhedrosis...

A 25K protein was a major component of the Triton X-100 solubilized fraction prepared for the isolation of nuclear matrices from Spodoptera frugiperda cells infected with Autographa californica nuclear polyhedrosis virus (AcMNPV). Polyclonal antisera to p25 were produced in rabbits and used in the characterization of p25. Western blots of proteins probed with the p25 antiserum demonstrated the presence of the p25 in both the polyhedral-derived and extracellular viral phenotypes. Using an indirect fluorescent antibody assay, p25 was detected within the infected host cell as early as 6 h p.i. and throughout the time course examined. The intensity in fluorescence increased from the periphery of the infected cells to within the nucleus at late times post-infection. On electron micrographs, the p25 was observed as dense gold particles in localized pockets and around virions in the nucleus at 16 and 36 h p.i., respectively. By 48 h p.i., p25 was concentrated over the surface of nucleocapsids in the intranuclear region and within polyhedra. p25 was not associated with any infected cell structures and did not appear to be involved in polyhedron formation. These studies demonstrated that p25 was a structural protein which was expressed very early during infection and displayed characteristics similar to In major capsid proteins of the baculoviruses.