Figure 2. Models for Env incorporation.
The passive model assumes that HIV-1 buds from the membrane and simply carries with it any Env that may be present. In the cotargeting model, incorporation is enhanced by targeting both Gag and Env to raft-like regions within the PM. The direct Gag–Env interaction model proposes that the motifs within MA and gp41 that have been demonstrated to influence Env incorporation comprise interaction domains, and that this interaction (circled) is required for Env incorporation into particles. The indirect Gag-Env interaction model posits the existence of a bridging factor and explains the observation that the requirement for the gp41 CT in Env incorporation is cell type dependent. MA, grey; gp120, blue; gp41, green; gp41 transmembrane domain, yellow; lipid rafts, red; hypothetical bridging factor, pink. Note that for simplicity the Env complex is shown as monomer (one molecule each of gp120 and gp41) rather than in its native trimeric state. This figure is adapted from Checkley et al. [4].