polyproteinen

Polyproteins are long polypeptides translated from a single open reading frame that are proteolytically cleaved to form multiple mature proteins. This strategy is common in many RNA viruses and allows compact genomes to encode several functional units while maintaining coordinated expression and stoichiometry. Production typically begins with translation of a single polyprotein, containing sequences for several structural and nonstructural proteins. Specific proteases, often virus-encoded, cut the polyprotein at defined sites, yielding discrete proteins that assemble into viral particles or replication complexes. Some cleavages are co-translational, others post-translational, with sequential or coordinated processing.

In the viral realm, picornaviruses such as poliovirus and rhinovirus produce a single polyprotein that is processed into P1 (capsid proteins) and P2/P3 (nonstructural proteins). Flaviviruses such as dengue and Zika generate a single polyprotein cleaved into structural proteins and several nonstructural proteins. Coronaviruses translate ORF1a/1ab into lengthy polyproteins that are processed to yield 16 nonstructural proteins forming the replication-transcription complex. The polyprotein strategy provides efficient genome organization and coordinated maturation but creates vulnerability: inhibiting the responsible proteases can block replication and is a target for antivirals.

In non-viral biology, polyprotein production is far less common, but maturation of long precursors into multiple mature proteins is a general regulatory theme.