Host factor dependent lifecycle of positive strand RNA viruses

Positive strand RNA viruses utilize cellular translational machinery at the first step of viral infection. Cellular ribosomal complexes directly translate a viral genome RNA into a large protein by recognizing IRES that is a special genomic RNA region which recruits some translation initiation factors. Thereafter, this large protein is cleaved by some cellular proteases. This step produces viral core proteins, envelope proteins and proteases. These proteases specifically cleave the remaining viral protein, which produces several viral non-structural proteins. These non-structural proteins mainly contribute to viral RNA replication and pathogenesis. Thus, positive strand RNA viruses critically make the best use of cellular factors for their existence.