RETRIEVAL OF RESIDENT LATE-GOLGI MEMBRANE-PROTEINS FROM THE PREVACUOLAR COMPARTMENT OF SACCHAROMYCES-CEREVISIAE IS DEPENDENT ON THE FUNCTION OF GRD19P

The dynamic vesicle transport processes at the late-Golgi compartment of Saccharomyces cerevisiae (TGN) require dedicated mechanisms for cor rect localization of resident membrane proteins. In this study, we rep ort the identification of a new gene, GRD19, involved in the localizat ion of the model late-Golgi membrane protein A-ALP (consisting of the cytosolic domain of dipeptidyl aminopeptidase A [DPAP A] fused to the transmembrane and lumenal domains of the alkaline phosphatase [ALP]), which localizes to the yeast TGN, A grd19 null mutation causes rapid m islocalization of the late-Golgi membrane proteins A-ALP and Kex2p to the vacuole, In contrast to previously identified genes involved in la te-Golgi membrane protein localization, grd19 mutations cause only min or effects on vacuolar protein sorting, The recycling of the carboxype ptidase Y sorting receptor, Vps10p, between the TGN and the prevacuola r compartment is largely unaffected in grd19 Delta cells, Kinetic assa ys of A-ALP trafficking indicate that GRD19 is involved in the process of retrieval of A-ALP from the prevacuolar compartment, GRD19 encodes a small hydrophilic protein with a predominantly cytosolic distributi on. In a yeast mutant that accumulates an exaggerated form of the prev acuolar compartment (vps27), Grd19p was observed to localize to this c ompartment, Using an in vitro binding assay, Grd19p was found to inter act physically with the cytosolic domain of DPAP A, We conclude that G rd19p is a component of the retrieval machinery that functions by dire ct interaction with the cytosolic tails of certain TGN membrane protei ns during the sorting/budding process at the prevacuolar compartment.