N6 -Methyladenosine in Flaviviridae Viral RNA Genomes Regulates Infection

The RNA modification N6 -methyladenosine (m 6 A) post-transcriptionally regulates RNA function. The cellular machinery that controls m 6 A includes methyltransferases and demethylases that add or remove this modification, as well as m 6 A-binding YTHDF proteins that promote the translation or degradation of m 6 A-modified mRNA. We demonstrate that m 6 A modulates infection by hepatitis C virus (HCV). Depletion of m 6 A methyltransferases or an m 6 A demethylase, respectively, increases or decreases infectious HCV particle production. During HCV infection, YTHDF proteins relocalize to lipid droplets, sites of viral assembly, and their depletion increases infectious viral particles. We further mapped m 6 A sites across the HCV genome and determined that inactivating m 6 A in one viral genomic region increases viral titer without affecting RNA replication. Additional mapping of m 6 A on the RNA genomes of other Flaviviridae , including dengue, Zika, yellow fever, and West Nile virus, identifies conserved regions modified by m 6 A. Altogether, this work identifies m 6 A as a conserved regulatory mark across Flaviviridae genomes.