HIV rep start
The HIV replication cycle begins with binding of a viral particle to a susceptible cell. The HIV gp120 on the viral particle binds to cellular CD4 (Movie 8), explaining the tropism of HIV for CD4+ cells. The gp120 protein also binds to a second host encoded cell surface protein, which acts as a coreceptor, either CXCR4 (Movie 11)(Feng et al. 1996) or CCR5(Alkhatib et al. 1996; Deng et al. 1996; Doranz et al. 1996).
After binding, membrane fusion takes place, mediated by the gp41 component of the viral envelope spike (Movie 9). Fusion makes the lipid bilayer of the viral particle continuous with that of the infection target cell, so that the viral core complex can enter into the cytoplasm.