Figure 1. Cellular trafficking pathways governed by Vps-C complexes.
The vacuole is the terminal organelle in the yeast endocytic pathway, equivalent to the mammalian lysosome. Vps-C complexes regulate several transport routes to and from the vacuole: (A) vacuoles fuse homotypically in response to environmental signals and during cell division and cell fusion; (B) endocytic vesicles and early endosomes fuse homotypically as they mature; (C) transport vesicles derived from the TGN fuse with endosomes to deliver biosynthetic cargos; (D) late endosome cargo is delivered to the vacuole via heterotypic fusion; (D′) Retrograde traffic from the vacuole passes through the endosome; (E) some vacuole-resident proteins are transported from TGN to vacuole in an AP-3-dependent pathway that bypasses endosomes; and (F) soluble cargos and defective organelles are transported from the cytosol into the vacuole lumen via the CVT and autophagy pathways. Solid arrows depict transport steps thought to require Vps-C complexes. Endosomes and endosomal trafficking events requiring CORVET are depicted in purple, while vacuoles and vacuolar trafficking events requiring HOPS are depicted in red. While this model depicts traffic in yeast, endolysosomal traffic in plants, invertebrates and mammals is broadly similar. AP-3, adaptor protein-3 complex; TGN, trans-Golgi network; CVT, cytoplasm to vacuole targeting; HOPS, fusion and vacuole protein sorting; CORVET, class C core vacuole/endosome tethering complex.