Translation of Senecavirus A polyprotein is initiated from the IRES-proximal initiation codon

To clarify whether Senecavirus A (SVA) has the potential of alternative translation, an extra G residue was inserted into an SVA cDNA clone, resultantly generating an "AUGAUG" motif. The second AUG is the authentic SVA initiation codon, whereas the first AUG is a putative one. Subsequently, eighteen nucleotides were inserted one by one between AUG and AUG for reconstructing cDNA clones. The test of virus recovery showed that three replication-competent SVAs, whose AUG/AUG-flanked sequences were not multiples of three nucleotides, were successfully rescued from their individual cDNA clones. The wild-type SVA possesses a UUUUU motif within the polyprotein-encoding region. Sanger sequencing showed that these three replication-competent SVAs harbored one or two extra U residues in the UUUUU motif, implying that polyprotein translation was initiated from the putative AUG, and the authentic AUG would be inactivated. This is probably attributed to the lack of ribosome scanning along an SVA genome.