RNA viruses rely on the host-donated factors for replication and transcription of their genomic RNAs. In some RNA viruses, the virus-encoded RNA-dependent RNA polymerase (RdRp) forms a complex with host-donated translational factors. The formation of a complex between the virus-encoded RdRps and the host-donated translational factors is required for RNA replication and transcription of viral genomic RNAs in the host cells. We have determined the complex structure of Qβ virus RdRp and host-donated translational elongation factors. This is the first complex structure of virus RdRp and host-donated proteins. The structure has clarified detailed mechanisms for assembly of an active complex of Qβ virus RdRp with host-donated translational factors, and suggested new functions of host translational factors beyond their established functions in the cell.