Evidence that untranslated genomic sequences are key determinants of insect-specific flavivirus host restriction

Most flaviviruses cycle between arthropods and vertebrates. Others, such as Long Pine Key virus (LPKV), are insect-specific. We investigated whether untranslated sequences in the genome of LPKV are critical determinants of its host restriction. A chimeric virus was created by inserting the entire 5′ and 3′ untranslated regions and capsid gene of LPKV into the genetic backbone of Zika virus (ZIKV). The virus replicated in mosquito cells, but not vertebrate cells. Three additional chimeras were created by exchanging specific regions in the 5′ and 3' untranslated regions of ZIKV with the corresponding regions of LPKV. A chimera that contained stem loop A (the viral promoter) of LPKV in the genetic background of ZIKV produced virus that replicated in both mosquito and vertebrate cells. These data suggest that the ZIKV NS5 polymerase recognizes the LPKV promoter and that untranslated genomic elements, other than SLA, are key determinants of insect-specific flavivirus host-specificity.