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2A Protease Is Not a Prerequisite for Poliovirus Replication

ABSTRACT Poliovirus (PV) 2Apro has been considered important for PV replication and is known to be toxic to host cells. A 2Apro-deficient PV would potentially be less toxic and ideal as a vector. To examine whether 2Apro is needed to form progeny virus, a full-length cDNA of dicistronic (dc) PV with (pOME) or without (pOMEΔ2A) 2Apro 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 2Apro 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 2Apro 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 2Apro (pOMΔP1Δ2A) or without both 2Apro 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 2Apro 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 2Apro-deficient PV can be used as a vector, a P1-null PV containing the enhanced green fluorescent protein (EGFP) coding sequence with or without 2Apro was examined. It expressed fluorescent protein. This result suggests that 2Apro-deficient PV can express foreign genes.