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J. Cell Biol.,
Volume 140, Number 3, February 9, 1998 577-590
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229
The dynamic vesicle transport processes at
the late-Golgi compartment of Saccharomyces cerevisiae (TGN) require dedicated mechanisms for correct
localization of resident membrane proteins. In this
study, we report the identification of a new gene,
GRD19, involved in the localization 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 mislocalization of the late-Golgi membrane proteins
A-ALP and Kex2p to the vacuole. In contrast to previously identified genes involved in late-Golgi membrane
protein localization, grd19 mutations cause only minor effects on vacuolar protein sorting. The recycling of the
carboxypeptidase Y sorting receptor, Vps10p, between
the TGN and the prevacuolar compartment is largely
unaffected in grd19
cells. Kinetic assays 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 distribution. In a yeast
mutant that accumulates an exaggerated form of the
prevacuolar compartment (vps27), Grd19p was observed to localize to this compartment. Using an in
vitro binding assay, Grd19p was found to interact physically with the cytosolic domain of DPAP A. We conclude that Grd19p is a component of the retrieval machinery that functions by direct interaction with the
cytosolic tails of certain TGN membrane proteins during the sorting/budding process at the prevacuolar compartment.
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