Clathrin-coated vesicles (CCVs) are formed at the plasma membrane and act as 
vectors for endocytosis. They also assemble at the trans-Golgi network (TGN), 
but their exact function at this organelle is unclear. Recent studies have 
examined the effects on vacuolar and secretory protein transport of knockout 
mutations of the adaptor protein 1 (AP1) μ-adaptin subunit AP1M, but these 
investigations do not clarify the situation. These mutations lead to the 
abrogation of multiple trafficking pathways at the TGN and cannot be used as 
evidence in favour of CCVs being agents for receptor-mediated export of vacuolar 
proteins out of the TGN. This transport process could just as easily occur 
through the maturation of the TGN into intermediate compartments that 
subsequently fuse with the vacuole.