Figure 2.

Each assembly-defective Gag mutant is arrested at a characteristic point in the HIV-1 capsid assembly pathway. Initial studies in the cell-free system and in HIV-1-expressing cells revealed that Gag progresses through a stepwise pathway of multiprotein complexes defined as intermediates in a pathway of assembly based on pulse-chase experiments (reviewed in [47])). Subsequent experiments confirmed the order of intermediates in this pathway by showing that each assembly-defective Gag mutant is arrested at a characteristic point in this pathway. Altogether five different categories of mutants have been identified (Class 1–5), one for each point in the pathway. The difference between Class 3 and Class 4 being that Class 3 mutants are arrested as cytosolic ~80S complexes while Class 4 mutants are arrested as PM-associated ~80S complexes, suggesting that the ~80S assembly intermediate is the complex in which assembling Gag traffics from the cytosol to the PM. Later studies identified some of the host proteins in the assembly intermediates. Relevant references are in the text.