The HIV-1 assembly machine.

Abstract

HIV-1 like all retroviruses is released by budding from the host cells surface and thereby acquires a plasma membrane-derived lipid envelope that provides a tight seal and shields the virus from the environment. Budding also offers a non-lytic pathway for virus egress and thus has the advantage that the infected cell remains viable and can continue to produce progeny virions. HIV-1 particle assembly and budding are directed by the Gag polyprotein the precursor for the internal structural components of the mature virion which are matrix (MA) capsid (CA) nucleocapsid (NC) and p6. The Gag polyprotein coordinates the late stages of the replication cycle by bringing together all the building blocks of the virion and is sufficient to organize the efficient assembly and release of virus-like particles even when expressed in the absence of other viral proteins. Initially the polymerization of Gag polyproteins leads to the formation of an immature particle with a relatively stable spherical shell underneath the virion envelope. However for the virion to become infectious a maturation step is required that results in a suitably metastable capsid that can be disassembled within a target cell to release the viral genome. For maturation to occur the Gag polyprotein must be cleaved by the viral protease which triggers a large-scale rearrangement of the cleavage products within the assembled particle and a dramatic structural transition from a spherical to a conical capsid [1-4]. (excerpt)