Multiple sorting pathways between the late Golgi and the vacuole in yeast

Newly synthesized proteins that reach the last compartment of the Golgi complex can be sorted into pathways leading either to the cell surface or to the vacuole. It now appears that there are at least two routes from the Golgi to the vacuole: the 'CPY pathway', which involves transit through an endosomal/prevacuolar compartment (PVC), and a recently discovered 'ALP pathway', which bypasses the PVC, but may involve other as yet unidentified intermediate compartments. No cytosolic signal has been identified that directs the entry of membrane proteins into the CPY pathway. In contrast, the transport of ALP through the ALP pathway is saturable and signal mediated. Much recent work has focused on the identification of proteins that regulate trafficking to the vacuole. A number of genes have been identified that are specific for either the CPY or ALP sorting pathways, while other genes affect both types of transport and may therefore act at or after a point of convergence. Progress has also been made in further elucidating the members of the SNARE complexes that act in Golgi-to-PVC transport as well as those that mediate fusion with the vacuole.