Endocytosis and trans-Golgi Network in Yeast.

Endocytosis is the process by which cells internalize extracellular materials, cell surface proteins, and lipids via vesicles formed by membrane invagination. Endocytosed cargos are first delivered to sorting compartments and then recycled back to the plasma membrane or brought to late endosomal compartments en route to the lysosome/vacuole for degradation. The budding yeast Saccharomyces cerevisiae has been an important model organism for studying the molecular mechanisms involved in the multi-step process of the endocytic pathway, including clathrin-coated vesicle formation, vesicle internalization, cargo sorting, recycling, and degradation. In the yeast endocytic pathway, the mechanisms of formation and internalization of clathrin-coated vesicles are well conserved in relation to those in mammalian cells. Yeast also has mechanisms similar to those in mammalian cells for the regulation of events in the endo-lysosomal pathway, such as endosome maturation, multi-vesicular body formation, and retrograde transport. In contrast, the structure and properties of the endocytic sorting compartment in yeast differ significantly from those in mammalian cells. Recent studies have revealed that a sub-region within the trans-Golgi network (TGN) acts as a sorting compartment in yeast. In this chapter, we summarize recent findings regarding the molecular mechanisms of the endocytic pathway, particularly the involvement of the TGN.