Figure 5.

Models for virus membrane fission. (A) “Purse-string” model based on data from Saksena et al. (2009). A single ESCRT-III filament (red) with asymmetric ends (blue/green) is used to delineate and later constrict the neck of an evolving vesicle. Vps4 is proposed to disassemble the filament from one end to constrict the string, but Vps4-independent sliding may also achieve this constriction. (B) “Spiral constriction” model based on data from Lata et al. (2008). A growing ESCRT-III spiral surrounds and eventually constricts a cargo-containing membrane domain, forcing cargo at the center into an evolving vesicle. Membrane scission has been suggested to be mediated by membrane adhesion on a dome-like protein scaffold formed by the ESCRT-III complex (Fabrikant et al. 2009).