The curvature of host cell membranes during the budding of HIV viruses occurs by an opposite topology, as compared to endocytosis and phagocytosis phenomena. This topology of vesicle formation is indeed observed during the formation of internal vesicles of late endosomal compartments called multivesicular bodies (MVB). Formation of these vesicles is controlled by ubiquitylation and the recruitment of the endosomal sorting complex required for transport (ESCRT). The sorting of HIV-1 structural protein Pr55gag into the viral bud requires the recruitment of the ESCRT complex, potentiated by Pr55gag ubiquitylation. Interestingly, in response to viral infection, type I interferon triggers the expression of the ubiquitin-like polypeptide ISG15 which then inhibits the recruitment of the ESCRT machinery by inhibiting Pr55gag ubiquitylation.