The Mechanism Of RNA Virus Replication And Evasion Of Innate Antiviral Immunity

RNA remodeling proteins play an important role in refolding RNA to form proper RNA structures.RNA remodeling proteins are comprised of two groups of proteins: ATP-dependent RNA helicases and ATP-independent RNA chaperones.The genome of RNA viurses are usually formed complex dsRNA structure,so it is necessary for virus encoded RNA helicases/chaperones to unwind the duplex templates and make sure that the RNA replication is smoothly initiated.There are many studies about positive-stranded RNA virus-encoded helicases,while little is known about the helicases of negative-stranded RNA virus.VSV is an enveloped negative-stranded RNA virus.It consists of a 11 kb long genome,which encodes 5 proteins,including nucleocapsid(N),phosphoprotein(P),large polymerase(L),matrix(M),and surface glycoprotein(G).The packaged P and L proteins form the RNA-dependent RNA polymerase complex of VSV with N protein binding to RNA genome.The M protein plays multiple regulatory roles in viral particle assembly.G protein is enveloped on virus coated with multiple copies of trimeric surface.We found that VSV G have NTPase and helicase activity.It displays the 5′ to 3′ and 3′ to 5′ direction of unwinding.VSV G also has an ATP-independent RNA chaperone activity,which can destabilize structured RNA strands and stimulate RNA strand annealing.Moreover,VSV G can help RdRP to facilitate VSV RNA replication as a co-factor,which plays an important role in viral life cycle.Overall,our findings uncover that VSV G protein contains the RNA helicase and chaperoning activities and plays the important role in viral RNA replication.RNAi is an evolutionarily conserved post-transcriptional gene silencing mechanism in eukaryotes and has been well recognized as an antiviral immunity in fungi,plants,and invertebrates.In the process of antiviral RNAi,viral dsRNA replicative intermediates generated during RNA virus replication are recognized and processed by Dicer into siRNAs.These virus-derived siRNAs(vsiRNAs)are then transferred into RNA-induced silencing complex(RISC),to direct the cleavage of cognate viral RNAs.RNAi can also function as an antiviral defense in mammals.Interesting,virus can encode a viral suppressor of RNA silencing to antagonize RNAi.HCV is a non-enveloped positive-stranded RNA virus.The viral genome of HCV constitutes a 9.5 kb RNA which encodes three structural(core,E1 and E2)and six nonstructural proteins(NS2,NS3,NS4 A,NS4B,NS5 A,NS5B).The core protein constitutes the viral nucleocapsid;as a protease,NS3 also contains RNA helicase and RNA-stimulated NTPase activities;NS5A is a phosphoprotein,which inhibiting PKR;NS5B,a RNA-dependent RNA polymerase(RdRp),is the key enzyme responsible for HCV RNA replication.In this study,the nonstructural protein NS2 of HCV as the viral suppressor of RNAi(VSR)evades antiviral RNAi.We identified that NS2 as a VSR inhibits Dicer-mediated siRNA biogenesis by sequestrating dsRNA.We also found that the key point mutations,which can impair the NS2-mediated suppression of RNAi.Our findings provide a theoretical basis for designing new antiviral drugs directly targeting NS2.