In vitro assembly of poliovirus empty capsids: antigenic consequences and immunological assay of the morphopoietic factor.

The assembly of poliovirus 14 S particles into empty capsids was studied without cell extract (self-assembly) and in extracts of infected or uninfected HeLa cells. The products were analyzed using monoclonal antibodies specific for N1, N2, or H epitopes. The empty capsids formed in infected cell extract, and only those, possessed N2 epitopes like the procapsids formed in vivo, thus showing that a virally encoded or induced factor determines the antigenicity of the assembly product. Based on this observation, a simple immunological assay for the activity of the morphopoietic factor is presented. This factor is shown to lack serotype specificity.