ABSTRACT

Poliovirus (PV) 2A^pro has been considered important for PV replication and is known to be toxic to host cells. A 2A^pro-deficient PV would potentially be less toxic and ideal as a vector. To examine whether 2A^pro is needed to form progeny virus, a full-length cDNA of dicistronic (dc) PV with (pOME) or without (pOMEΔ2A) 2A^pro was constructed in the strain PV1(M)OM. RNAs of both pOME and pOMEΔ2A were capable of forming progeny viruses, called OME and OMEΔ2A, respectively. In their ability to induce a cytopathic effect (CPE), the strains ranked as OMEΔ2A < OME ≒ PV1(M)OM. These results suggest that 2A^pro is not essential for full-length dc PV to form progeny virus and that it contributes to the efficient viral replication and/or induction of a CPE. To clarify whether 2A^pro is essential for P1-null (lacking the entire coding sequence for capsid proteins) PV, the RNA replication activity of P1-null PV (pOMΔP1) or P1-null PV without 2A^pro (pOMΔP1Δ2A) or without both 2A^pro and 2B (pOMΔP1Δ2AΔ2B) was examined. The RNAs of pOMΔP1 and pOMΔP1Δ2A could replicate and form progeny viruses under a trans supply of P1 protein, whereas the RNA of pOMΔP1Δ2AΔ2B could not. These results suggest that 2A^pro is not needed for the replication of P1-null PV, although it is important for PV RNA replication and inducing a CPE. To know whether a 2A^pro-deficient PV can be used as a vector, a P1-null PV containing the enhanced green fluorescent protein (EGFP) coding sequence with or without 2A^pro was examined. It expressed fluorescent protein. This result suggests that 2A^pro-deficient PV can express foreign genes.