Plant virus RNAs. Coordinated recruitment of conserved host functions by (+) ssRNA viruses during early infection events

Abstract

Positive-sense single-stranded RNA viruses have developed strategies to exploit cellular resources at the expense of host mRNAs. The genomes of these viruses display a variety of structures at their 5' and 3' ends that differentiate them from cellular mRNAs. Despite this structural diversity, viral RNAs are still circularized by juxtaposition of their 5' and 3' ends, similar to the process used by cellular mRNAs. Also reminiscent of the mechanisms used by host mRNAs, translation of viral RNAs involves the recruitment of translation initiation factors. However, the roles played by these factors likely differ from those played by cellular mRNAs. In keeping with the general parsimony typical of RNA viruses, these host factors also participate in viral RNA replication. However, the dual use of host factors requires that viral RNA template utilization be regulated to avoid conflict between replication and translation. The molecular composition of the large ribonucleoprotein complexes that form the viral RNA replication and translation machineries likely evolves over the course of infection to allow for switching template use from translation to replication.

Figure 1.

Interaction of the 3′ and 5′ ends of the RNA of (+) ssRNA viruses is mediated by RNA-RNA interactions or through the recruitment of host translation initiation factors. A, Simultaneous interactions between eIF4G-eIF4E and eIF4G-PABP result in a closed-loop conformation typical of cellular mRNAs. B, Direct RNA-RNA interactions circularize the uncapped and nonpolyadenylated RNA of viral genomic RNAs (e.g. BYDV). C, Rotaviral NSP3 interacts simultaneously with the nonpolyadenylated 3′ end of the viral RNA and with the cap-bound eIF4G. NSP3 is present in a complex with eIF4A and eIF4E. D, End-to-end interactions for the uncapped, polyadenylated poliovirus RNA occur via the host proteins PABP and PCBP and the viral poly(A) tail and IRES structure. E, RNA circularization of the RNA plant potyviruses might be mediated by eIF4G, eIF4E, PABP, and VPg interactions.