polyprotein

Polyprotein is a single long polypeptide encoded by a gene that is subsequently cleaved by proteases to form multiple functional proteins. In many RNA viruses, the genome is translated as one or more polyproteins that are processed into structural and nonstructural components essential for replication and virion assembly.

A positive-sense RNA genome typically acts as mRNA, enabling translation of a long polyprotein. Viral proteases, and sometimes host proteases, cleave this polyprotein at conserved sites to yield mature proteins. Cleavage can occur during translation or after, producing the correct stoichiometry and timing of component proteins.

Examples include picornaviruses such as poliovirus, where a single polyprotein is cleaved into structural (P1) and nonstructural (P2) regions; flaviviruses such as dengue, which generate C, prM/M, E and multiple NS proteins; and coronaviruses, which translate replicase polyproteins pp1a and pp1ab and cleave them with viral proteases to produce nsps.

Polyproteins allow compact genome organization and coordinated production of many enzymes from a single transcript. Their processing is a major target for antiviral drugs, particularly inhibitors of viral proteases. The concept is mainly applied to viral genomes; in cellular biology, polyproteins are less common as mature products.