An efficient complementation system for replication of defective poliovirus mutants.

Unlabelled: The picornavirus genome encodes a large, single polyprotein that is processed by viral proteases to form an active replication complex. The replication complex is formed with the viral genome, host proteins, and viral proteins that are produced/translated directly from each of the viral genomes (viral proteins provided in ). Efficient complementation of replication complex formation by viral proteins provided in , thus exogenous or ectopically expressed viral proteins, remains to be demonstrated. Here, we report an efficient complementation system for the replication of defective poliovirus (PV) mutants by a viral polyprotein precursor in HEK293 cells. Viral 3AB in the polyprotein, but not 2BC, was processed exclusively in . Replication of a defective PV replicon mutant, with a disrupted cleavage site for viral 3C protease between 3C and 3D (3C/D[A/G] mutant) could be rescued by a viral polyprotein provided in . Only a defect of 3D activity of the replicon could be rescued in ; inactivating mutations in 2C, 3B, and 3C of the replicon completely abrogated the -rescued replication. An intact N-terminus of the 3C domain of the 3CD provided in was essential for the -active function. By using this complementation system, a high-titer defective PV pseudovirus (PV) (>10 infectious units per mL) could be produced with the defective mutants, whose replication was completely dependent on complementation. This work reveals potential roles of exogenous viral proteins in PV replication and offers insights into protein/protein interaction during picornavirus infection.

Importance: Viral polyprotein processing is an elaborately controlled step by viral proteases encoded in the polyprotein; fully processed proteins and processing intermediates need to be correctly produced for replication, which can be detrimentally affected even by a small modification of the polyprotein. Purified/isolated viral proteins can retain their enzymatic activities required for viral replication, such as protease, helicase, polymerase, etc. However, when these proteins of picornavirus are exogenously provided (provided in ) to the viral replication complex with a defective viral genome, replication is generally not rescued/complemented, suggesting the importance of viral proteins endogenously provided (provided in ) to the replication complex. In this study, I discovered that only the viral polymerase activity of poliovirus (PV) (the typical member of picornavirus family) could be efficiently rescued by exogenously expressed viral proteins. The current study reveals potential roles for exogenous viral proteins in viral replication and offers insights into interactions during picornavirus infection.