2A Protease Is Not a Prerequisite for Poliovirus Replication

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 (pOME Delta 2A) 2A(pro) was constructed in the strain PV1(M)OM. RNAs of both pOME and pOME Delta 2A were capable of forming progeny viruses, called OME and OME Delta 2A, respectively. In their ability to induce a cytopathic effect (CPE), the strains ranked as OME Delta 2A < OME is approximately equal to 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 (pOM Delta P1) or P1-null PV without 2A(pro) (pOM Delta P1 Delta 2A) or without both 2A(pro) and 2B (pOM Delta P1 Delta 2A Delta 2B) was examined. The RNAs of pOM Delta P1 and pOM Delta P1 Delta 2A could replicate and form progeny viruses under a trans supply of P1 protein, whereas the RNA of pOM Delta P1 Delta 2A Delta 2B 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.