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. Author manuscript; available in PMC: 2011 Feb 1.
Published in final edited form as: Nat Rev Mol Cell Biol. 2010 Jun 30;11(8):556–566. doi: 10.1038/nrm2937

Figure 5.

Figure 5

Membrane scission by ESCRT-III. a. Imaging of Snf7 in the act of membrane scission at a bud neck in vitro, reproduced by permission from27. The merged image at top combines red (membrane, rhodamine), blue (ubiquitylated cargo, CFP) and green (Snf7, Alexa 488) channels. The lower panel shows a close-up of the membrane bud, with the arrow highlighting the localization of Snf7 to the bud neck. ESCRT-I, -II, and Vps20 are present but not labeled in this experiment. b. Cartoon for scission, inspired by spiral SNF7 structures21. At top, a molecule of Vps20 initiates ESCRT-III assembly. In yeast cells, at least two copies of Vps20 are required to initiate the scission-competent assembly of ESCRT-III53,56. At 3 o'clock, multiple Snf7 molecules57 polymerize downstream of Vps20. At bottom, one or a few molecules of Vps24 and Vps2 close the spiral, with only Vps24 minimally required for scission. At 9 o'clock, Vps4 breaks up the ESCRT-III polymer at the expense of ATP hydrolysis. c. Integration of budding and scission. After assembling in the bud neck as depicted in Fig. 4, the working model postulates that the ESCRT-III spiral assembles on the bud-proximal side of ESCRT-II to carry out scission.