Polyprotein Processing as a Strategy for Gene Expression in RNA Viruses

RNA viruses in many families and genera express their genomes in ways which involve the synthesis and subsequent cleavage of precursor polyproteins. This strategem allows the activation of subsets of proteins with different biochemical functions from the same precursor protein. Although the virus-encoded enzymes responsible for processing the polyproteins are structurally diverse, they are all highly specific for their substrates. The resulting processing cascade is a tightly controlled process, which in several cases involves the action of protein cofactors to modulate the activity of the proteinase.