Subgenomic flavivirus RNA binds the mosquito DEAD/H-box helicase ME31B and determines Zika virus transmission by Aedes aegypti

Significance Mosquito-transmitted flaviviruses such as Zika virus (ZIKV) are responsible for over 400 million human infections each year. Unfortunately, the molecular mechanisms that facilitate flavivirus transmission by mosquitoes remain unclear. Here, we demonstrate that noncoding subgenomic flavivirus RNA (sfRNA), that is produced by all flaviviruses, plays a critical role in ZIKV transmission byAedes aegypti mosquitoes. ZIKV requires sfRNA to overcome the mosquito midgut barrier and efficiently accumulate in the mosquito saliva. We reveal that the mosquito protein ME31B has antiviral activity and specifically binds to sfRNA. These results establish sfRNA as a determinant of ZIKV transmission by mosquitoes and provide mechanistic insights into the functions of this noncoding RNA.