Different Degrees of 5'-3' DAR Interactions Modulate Zika Virus Genome Cyclization and Host Specific Replication.

Mosquito-borne flaviviruses, which include many important human pathogens such as West Nile virus (WNV), Dengue virus (DENV) and Zika virus (ZIKV), had caused numerous emerging epidemics in recent years. Knowledge on the viral genome functions necessary for effective viral replication in mosquito and vertebrate hosts remained obscure. Here, using ZIKV as a model, we found that the conserved downstream of AUG region (DAR), which is known as an essential element for the genome cyclization, involved in viral replication in a host specific manner. Mutational analysis of the DAR element showed that a single-nucleotide mismatch between 5'DAR-3'DAR had little effect on ZIKV replication in mammalian cells, but dramatically impaired viral propagation in mosquito cells. The revertant viruses passaged in mosquito cells generated compensatory mutations restoring the base pairing of DAR, further confirming the importance of the complementarity of DAR in mosquito cells. We demonstrated that a single nucleotide mutation in DAR is sufficient to destroy long-range RNA interaction of ZIKV genome, and affects de novo RNA synthesis at 28 °C instead of 37 °C, resulting in the different replication efficiencies of the mutant viruses in mosquito and mammalian cells. Our results reveal a novel function of the circular form of flavivirus genome in host-specific viral replication, providing new ideas to further explore the functions of viral genome during host adaptation. [ABSTRACT FROM AUTHOR]