Genetic analysis of a poliovirus/hepatitis C virus (HCV) chimera:: Interaction between the poliovirus cloverleaf and a sequence in the HCV 5′ nontranslated region results in a replication phenotype

Internal ribosomal entry sites (IRESs) can function in foreign viral genomes or in artificial dicistronic mRNAs. We describe an interaction between the wild-type hepatitis C virus (HCV)-specific sequence and the poliovirus (PV) 5'-terminal cloverleaf in a PV/HCV chimeric virus (containing the HCV IRES), resulting in a replication phenotype. Either a point mutation at nucleotide (nt) 29 or a deletion up to nt 40 in the HCV 5' nontranslated region relieved the replication block, yielding PV/HCV variants replicating to high titers. Fortuitous yet crippling interactions between an IRES and surrounding heterologous RNA must be considered when IRES-based dicistronic expression vectors are being constructed.