Hepatitis E virus RNA-dependent RNA polymerase: RNA template specificities, recruitment and synthesis.

Hepatitis E virus (HEV) is a positive-sense RNA virus and member of the genus Orthohepevirus in the family Hepeviridae. Although HEV RNA-dependent RNA polymerase (HEV-RdRp) plays an important role in the HEV life cycle, its template specificities are not completely understood. We expressed HEV-RdRp protein with His-tag in a bacterial system and analysed template specificities using different putative cis-regulatory elements in the HEV genome. The enzyme showed highest affinity for the 3' non-coding region (NCR), then for the 5'NCR and least for the putative subgenomic promoter (SgP). The enzyme could co-bind to 3'NCR and putative SgP templates together, as evident from the supershift in binding assay, indicating presence of different binding sites for these elements. Proteomic analysis revealed that the RNA elements share two common peptides for binding, while a third peptide, which is highly conserved across different HEV genotypes, is specific for 3'NCR. We propose that, during the early phases of replication, as negative sense antigenome copies accumulate at the replication site, they probably initiate promoter swapping from 3'NCR to SgP, to favour synthesis of subgenomic RNA and to prevent synthesis of genomic RNA. The conserved site for 3'NCR binding could be potential antiviral target and needs further evaluation.