Figure 2.

Virions and subviral particles (SVPs) use two different pathways for secretion (adapted from Prange 2012). Capsids are released through budding into multivesicular bodies (MVBs) using endosomal sorting complex required for transport (ESCRT)-0, -I, -II, -III, and Vsp4 protein complexes (Katzmann et al. 2002; Hanson and Cashikar 2012). Envelope proteins facilitate budding of the viral capsids at the MVB membrane; however, it is unclear how envelope proteins are transported from the pre-Golgi/endoplasmic reticulum (ER) membrane to the late endosome. Nonenveloped particles are hypothesized to be released in an ESCRT-independent pathway that uses the apoptosis-linked gene 2 (ALG2)-interacting protein X (Alix), also implicated in the secretion of enveloped particles (Watanabe et al. 2007; Bardens et al. 2011). It is not clear how capsid particles distinguish between pathways of enveloped and nonenveloped release. ERGIC, ER-Golgi intermediate compartment.