Models for membrane scission mediated by endosomal sorting complex required for transport III (ESCRT-III). In both models, the HIV-1 Gag protein interacts with ESCRT-I and ALG2-interacting protein X(ALIX), which recruit ESCRT-III. Membrane scission is driven by ESCRT-III polymerization in concert with the activity of the AAA ATPase vacuolar protein sorting 4 (VPS4). a | In the first model, ESCRT-III is localized within the budding particle70. b | In the second model, ESCRT-I and ALIX are located within the budding particle and recruit ESCRT-III and VPS4, which are mostly located outside the budding particle. Env, envelope. Part a adapted from Van Engelenburg, S. B. et al. Distribution of ESCRT machinery at HIV assembly sites reveals virus scaffolding of ESCRT subunits. Science
343,653–656 (2014). Reprinted with permission from AAAS. Part b adapted from REF 117, © Cashikar et al.