Functional Coupling between Replication and Packaging of Poliovirus Replicon RNA

Abstract

Poliovirus RNA genomes that contained deletions in the capsid-coding regions were synthesized in monkey kidney cells that constitutively expressed T7 RNA polymerase. These replication-competent subgenomic RNAs, or replicons (G. Kaplan and V. R. Racaniello, J. Virol. 62:1687–1696, 1988), were encapsidated intrans by superinfecting polioviruses. When superinfecting poliovirus resistant to the antiviral compound guanidine was used, the RNA replication of the replicon RNAs could be inhibited independently of the RNA replication of the guanidine-resistant helper virus. Inhibiting the replication of the replicon RNA also profoundly inhibited its trans-encapsidation, even though the capsid proteins present in the cells could efficiently encapsidate the helper virus. The observed coupling between RNA replication and RNA packaging could account for the specificity of poliovirus RNA packaging in infected cells and the observed effects of mutations in the coding regions of nonstructural proteins on virion morphogenesis. It is suggested that this coupling results from direct interactions between the RNA replication machinery and the capsid proteins. The coupling of RNA packaging to RNA replication and of RNA replication to translation (J. E. Novak and K. Kirkegaard, Genes Dev. 8:1726–1737, 1994) could serve as mechanisms for late proofreading of poliovirus RNA, allowing only those RNA genomes capable of translating a full complement of functional RNA replication proteins to be propagated.

A Functional Link between RNA Replication and Virion Assembly in the Potyvirus Plum Pox Virus

“…The previously shown in vivo interaction between NIb and CP from PPV (49) argues in favor of a connection between replication and virion assembly. Although viral RNA incorporation into virions is independent of replication in the coronavirus Transmissible gastroenteritis virus (50), coupling between replication and packaging is not unusual in animal (51)(52)(53)(54) and plant (55) spherical viruses, where direct interactions between their corresponding viral capsid proteins and replicases were also detected (56,57). Hence, our results show that viral RNA replication is also required for the assembly of filamentous virions in a member of the family Potyviridae, the largest group of plant RNA viruses.…”

Coronavirus cis-Acting RNA Elements

“…To selectively package their genome RNA (rather than other viral and cellular RNAs), viruses employ distinct cis-acting sequences in the viral genome RNA and trans-acting viral factors (Annamalai and Rao, 2006;D'Souza and Summers, 2005;Nugent et al, 1999). Even though coronaviruses produce large amounts of subgenomic mRNAs in infected cells, these RNAs are not (or extremely inefficiently) incorporated into virus particles (Escors et al, 2003), suggesting that coronaviruses have evolved specific mechanisms to efficiently package their genome RNA into progeny virus particles.…”

Non-encapsidation activities of the capsid proteins of positive-strand RNA viruses

“…Current models suggest that viral replication proteins and viral RNAs are trafficked to these factories (Ahlquist, 2006). Although CPs of (+)-strand RNA viruses are not required to form the factories, viral genome encapsidation is functionally coupled to its replication for several viruses (Annamalai and Rao, 2006;Khromykh et al, 2001;Nugent et al, 1999;Venter et al, 2005). There is also growing evidence that CPs of multiple RNA viruses have an active role in viral RNA synthesis through binding of the viral RNA and/or interaction with viral RNA replication-associated proteins.…”