Use of the baculovirus system to assemble polyomavirus capsid-like particles with different polyomavirus structural proteins: analysis of the recombinant assembled capsid-like particles

The genes encoding the structural proteins VP1, VP2 and VP3) of murine poly omavirus were cloned into the p2Bac dual multiple cloning site vector, indi vidually or jointly, and the corresponding proteins were expressed in Spodo ptera frugiperda (Sf9) insect cells by cotransfecting Sf9 cells with the co nstructed vector and the linear DNA of Autographa californica multiple nucl ear polyhedrosis virus (AcMNPV). Recombinant capsid-like particles could be purified 5 days post-infection from Sf9 cells infected with AcMNPV-VP1, wi th or without the involvement of minor protein (VP2 or VP3). Although VP2 a nd VP3 alone could not generate recombinant particles, they became incorpor ated into these particles when expressed with VP1 in Sf9 cells. Recombinant particles with different polyomavirus structural protein(s) were obtained by using different combined expression of these proteins in Sf9 cells, Cell ular DNA of 5 kbp in size was packaged in all of the recombinant particles, which showed the same diameter as that of native virions. Agarose gel elec trophoresis indicated that DNA packaged in these recombinant particles had a different pattern than that of native virions. Two-dimensional gel electr ophoresis of the VP1 species of recombinant particles showed more VP1 speci es than those of the native virions from mouse cells and an additional spec ies of VP1 when VP2 was co-expressed with VP1. The recombinant particles we re also compared for their ability to compete for polyomavirus infection, T he competition assay indicated that the recombinant particles containing VP 2 were the most efficient in inhibiting the native polyomavirus infection o f 3T6 cells.