Upstream start codon in segment 4 of North American H2 avian influenza A viruses

▶ An upstream in-frame start codon was found in the H2 gene of North American avian influenza A viruses. ▶ The start is in a good Kozak context and in vivo assays using a reporter gene showed its efficient use. ▶ H2 leaders with an upstream start stimulated translation 2-3-fold compared to leaders without one. ▶ A clade of avian H2 viruses with potentially enhanced HA expression has been present since 1976.