Abstract
Insertion mutants of type 3 poliovirus (Sabin strain) were constructed that encode additional amino acid sequences at the level of residue 100 of the capsid polypeptide VP1 within the neutralization site 1, corresponding to a loop on the capsid surface. The addition of a tri- or hexapeptide did not hamper virus viability. The antigenic pattern of insertion mutants was only modified locally: all mutants lost reactivity of neutralization site 1 with the corresponding monoclonal antibodies, while the reactivity of sites 2 and 3 was unaffected by the insertion. We have shown for one of the mutants--vFG68--that the antigenic specificity of the neutralization site 1 was replaced by a new one. Although vFG68 differs from its parental Sabin strain only by the addition of three amino acids within VP1, neutralizing antibodies specific for vFG68 were induced by the native virion as well as by the heat-denatured mutated virions. Our results demonstrate that an oligopeptide of three or six amino acids can lengthen VP1 at the level of antigenic site 1 without affecting virus multiplication and that this foreign peptide is exposed on the virion surface.