polyproteins

Polyproteins are large polypeptides produced from a single open reading frame that are subsequently cleaved by proteolytic enzymes into multiple mature proteins. This strategy, common in viruses, allows a compact genome to encode several functions and enables regulated production of different proteins through specific cleavage events.

Many positive-sense RNA viruses translate their genomes as one long polyprotein, which is then cleaved at defined sites by viral proteases to yield structural proteins and nonstructural enzymes. Notable examples include poliovirus and other picornaviruses; hepatitis C virus (HCV); and retroviruses such as HIV, which produce Gag-Pol as a single polyprotein that is cleaved into mature components. Cleavage is directed by proteases such as picornaviral 2A and 3C proteases, HCV NS2-3/NS3-4A proteases, and the retroviral protease. In some systems, host proteases also contribute. The polyprotein approach economizes the genome and can coordinate the timing and quantity of expressed products, influencing virion assembly and replication.

In biotechnology and research, polyprotein concepts are used to express multiple proteins from one transcript. Strategies include engineered protease cleavage sites and self-cleaving peptide sequences (such as 2A peptides) that separate the individual proteins after translation, enabling coordinated expression of multiple components in a single reading frame.