Blocking RNA virus replication through the antiviral functions of cellular helicases. A recently emerging concept in innate immunity is the significant roles of cell-intrinsic restriction factors (CIRFs) against several viruses, which are expressed by the host cells. CIRFs greatly reduce virus replication and facilitate combating viruses and making the induced and passive innate immune responses more potent. The PI has identified cellular DEAD-box helicases as strong CIRFs against an RNA virus. RNA helicases are involved in all aspects of cellular metabolism and perform RNA duplex unwinding and remodeling of RNA-protein complexes in cells. Dissecting the mechanism of antiviral function of cellular helicases promises a new avenue to develop effective antiviral strategies against plant and possibly animal viruses Progress in our understanding of the mechanisms of host factors is greatly accelerated by the use of easily tractable virus - host systems, such as Tomato bushy stunt virus (TBSV) and yeast model. The PI will identify and characterize the most potent cellular helicases to block plant and insect virus replication. The proposal will focus on two cellular helicases that showed the most potent antiviral effect, thus justifying the potential of tis novel approach. The following are the major strengths of the proposal: (i) Viral RNA replication is clearly of immense importance for viruses to infect living organisms. (ii) The combination of yeast and authentic cell-free assay developed by the PI is currently the most potent for studying the mechanism of host factors involvement in viral RNA replication and viral pathogenesis. (iii) Cellular helicases are emerging as major cell-intrinsic restriction factors against several viruses (iv) This work has the potential to obtain a novel effective antiviral approach that has several advantages over traditional viral targets. The advantages include broader antiviral effects against many related and possibly even unrelated viruses and more durable antiviral effects. Developing an efficient antiviral strategy based on blocking viral replication via cellular helicass could rapidly be done in this elegant tombusvirus-yeast system. Based on the possible broad antiviral effect of these cellular helicases, which are highly conserved from plants to animals, research can then adapt the gained knowledge and methods for other animal, human and plant viruses. The research holds promise of benefiting society by leading to groundbreaking results in the area of virus replication, host-virus interactions and the adaptation of viruses to their hosts.