The role of proteolytic processing in the morphogenesis of virus particles.

Proteinases are encoded by many RNA viruses, all retroviruses and several DNA viruses. They play essential roles at various stages in viral replication, including the coordinated assembly and maturation of virions. Most of these enzymes belong to one of three (Ser, Cys or Asp) of the four major classes of proteinases, and have highly substrate-selective and cleavage specific activities. They can be thought of as playing one of two general roles in viral morphogenesis. Structural proteins are encoded by retroviruses and many RNA viruses as part of large polyproteins. Their proteolytic release is a prerequisite to particle assembly; consequent structural rearrangement of the capsid domains serves to regulate and direct association and assembly of capsid subunits. The second general role of proteolysis is in assembly-dependent maturation of virus particles, which is accompanied by the acquisition of infectivity.