Our report provides evidence supporting the idea of expression of core+1/ARFP in JFH1-based replicons and shows for the first time expression of core+1/ARFP from a 2a subtype strain; all previous studies were limited to studying exclusively genotype 1 isolates. Specifically, we show the expression of two forms of core+1/ARFP, designated core+1/L and core+1/S, with different kinetics of expression during the replication of the JFH1 replicon. Core+1/S was the predominant core+1 form during the early stages of replication, while core+1/L expression increased later in the replication cycle. Conversely, the lack of core+1 expression in the context of the chimeric H77/JFH1 replicon suggests novel translation mechanisms. It should be taken into account that the two isoforms may differ in some of their functions. For example, different isoforms of the hepatitis D virus delta antigen play roles in different stages of the viral replication cycle: the small delta antigen is necessary for replication, while the large delta antigen is produced at later stages and is involved in packaging. Core+1/ARFP isoforms produced by frameshift have been observed previously in cell-free systems. Our results strongly suggest that the core+1/ARFP/F isoform is not produced in the replicon system. Alternatively, our mutational analysis provides strong evidence that, in accordance with previous observations, codons 25/26 serve as translation initiator codons for core+1/ARFP/L, while codons 85/87 serve as translation initiator codons for core+1/S. The results of this study support the idea of expression of core+1 ORF in the context of the HCV replication, confirm the presence of alternative translation initiation mechanisms that are based on internal translation at codons 25/26 and 85/87, and unambiguously demonstrate the lack of frameshift at codons 8 to 11 which has long been speculated.
J Virol. 2015 May;89(9):5164-70. doi: 10.1128/JVI.02351-14.
Expression of the novel hepatitis C virus core+1/ARF protein in the context of JFH1-based replicons.