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FIG. 3. Model of HIV-1 assembly and budding through membrane rafts. gp160 trimerizes within the ER and, on reaching the TGN, associates with rafts because of its affinity for lipid rafts. It then migrates to the plasma membrane. Pr55gag and Pr160gag-pol oligomerize around two genomic RNAs and associate simultaneously with plasma membrane rafts due to the anchoring myristate and intrinsic properties of the MA domain. This allows the binding of MA to the cytoplasmic tail of glycoproteins. The cytoplasmic Nef protein, after palmitoylation, associates with the inner leaflet of the plasma membrane raft. The raft coalescence results in Nef incorporation into HIV-1 particles and in the enrichment of the envelope in lipid rafts. Then HIV-1 matures (cleavage of Gag precursors in MA, CA, NC, p6, and enzymes) and buds from the plasma membrane rafts. Nef protein is initially bound to membrane rafts. When encapsidated into HIV-1 particles, Nef is partly cleaved off by the viral protease into a soluble domain, which is thought to bind to the RNP. Membrane rafts are represented as shaded grey regions within the lipid bilayer.
