Description

The Gag protein is the major structural protein required for virus assembly. It is synthesized as a polyprotein in the cytosol of an infected cell and contains four functional segments: Matrix (MA), Capsid (CA), Nucleocapsid (NC), and p6. The NC region is flanked by two “spacer” segments, denoted SP1 and SP2. The polyprotein is all alpha helical, except the NC region, which is composed of two RNA interacting zinc knuckle domains.Human immunodeficiency virus (HIV) and other primate lentiviruses assemble at the plasma membrane and are released by budding from the cell surface. This mode of assembly allows the viral capsid to acquire a host cell-derived lipid envelope which protects it from the environment. HIV-1 assembly is controlled primarily by the Gag protein. Gag encodes the capsid proteins (group specific antigens), which are the core structural proteins of HIV. HIV Gag protein is encoded by the HIV gag gene, HXB2 nucleotides 790-2292. The precursor is the p55 myristoylated protein, which is processed to p17 (MAtrix), p24 (CApsid), p7 (NucleoCapsid), and p6 proteins, by the viral protease (PR). Gag associates with the plasma membrane, where virus assembly takes place. The 55-kDa Gag precursor is called assemblin to indicate its role in viral assembly.