The ESCRT machinery at a glance.

This article is part of a Minifocus on the ESCRT machinery. For further reading, please see related articles: ‘No strings attached: the ESCRT machinery in viral budding and cytokinesis’ by Bethan McDonald and Juan Martin-Serrano (J. Cell Sci. 122, 2167-2177) and ‘How do ESCRT proteins control autophagy?’ by Tor Erik Rusten and Harald Stenmark (J. Cell Sci. 122, 2179-2183). The endosomal sorting complex required for transport (ESCRT) machinery is conserved from Archaea to animals, and catalyzes the scission of membrane necks (Wollert et al., 2009) in the biogenesis of multivesicular bodies (MVBs) (Gruenberg and Stenmark, 2004; Hurley, 2008; Piper and Katzmann, 2007), cytokinesis (Carlton and Martin-Serrano, 2007; Lindas et al., 2008; Morita et al., 2007; Samson et al., 2008) and the budding of enveloped viruses such as HIV-1 (Bieniasz, 2006; Fujii et al., 2007; Morita and Sundquist, 2004). Cleavage occurs from the surface of the membrane that is contiguous with the inside of the membrane neck. The topology of scission mediated by the ESCRT machinery is opposite to that of the dynamin family of membrane-scission proteins, which cleave membrane necks by constricting them from the outside. The ESCRT machinery consists of the five protein complexes ESCRT-0, ESCRT-I, ESCRT-II, ESCRT-III and Vps4-Vta1, and several ESCRT-associated proteins (Hurley, 2008; Saksena et al., 2007; Williams and Urbe, 2007). ESCRT-0, ESCRT-I, ESCRT-II and Vps4-Vta1 are soluble complexes that move between cytosolic and membrane-bound states. By contrast, the subunits of ESCRT-III are soluble monomers that assemble on membranes into tightly bound filaments (Ghazi-Tabatabai et al., 2008), tubes (Hanson et al., 2008; Lata et al., 2008) and spirals (Hanson et al., 2008) that can only be released by the ATP-dependent action of Vps4-Vta1.