Mutagenesis Mapping of RNA Structures within the Foot-and-Mouth Disease Virus Genome Reveals Functional Elements Localised in the Polymerase (3Dpol) Encoding Region.

Abstract

AbstractRNA structure plays a crucial role in the replication of positive sense RNA viruses and can form functional elements within the untranslated regions (UTRs) and the protein coding sequences (or open reading frames (ORFs)). While RNA structures in the UTRs of several picornaviruses have been functionally characterised, the roles of putative RNA structures predicted for the ORF remain largely undefined. Here we have undertaken a bioinformatic analysis of the foot-and-mouth disease virus (FMDV) genome and predicted the existence of 53 evolutionarily conserved RNA structures within the ORF. Forty-five (45) of these structures were located in the regions encoding the non-structural proteins (nsps). To investigate if the structures in the regions encoding the nsps are required for FMDV replication we used a mutagenesis method, CDLR mapping, where sequential coding segments were shuffled to minimise RNA secondary structures while preserving protein coding, native dinucleotide frequencies and codon usage. To examine the impact of these changes on replicative fitness, mutated sequences were inserted into an FMDV sub-genomic replicon. We found that three of the RNA structures, all at the 3 termini of the FMDV ORF, were critical for replicon replication. Contrastingly, disruption of the other 42 conserved RNA structures that lie within the regions encoding the nsps had no effect on replicon replication, suggesting that these structures are not required for initiating translation or replication of viral RNA. Conserved RNA structures that are not essential for virus replication could provide ideal targets for the rational attenuation of a wide range of FMDV strains. ImportanceSome RNA structures formed by the genomes of RNA viruses are critical for viral replication. Our study shows that of 45 conserved RNA structures located within the regions of the foot-and-mouth disease virus (FMDV) genome that encode the non-structural proteins, only three are essential for replication of an FMDV sub-genomic replicon. Replicons replication is dependent on RNA translation and synthesis; thus, our results suggest that the three RNA structures are critical for either initiation of viral RNA translation and/or viral RNA synthesis. Although further studies are required to identify if the remaining 42 RNA structures have other roles in virus replication, they may provide targets for the rational large-scale attenuation of a wide range of FMDV strains. FMDV causes a highly contagious disease posing a constant threat to global livestock industries. Such weakened FMDV strains could be investigated as live-attenuated vaccines or could enhance biosecurity of conventional inactivated vaccine production.