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Vol. 13, Issue 9, 3078-3095, September 2002

Department of Biochemistry and Molecular Biology, University of
Minnesota Duluth School of Medicine, Duluth, Minnesota 55812
Golgi-localized
-ear homology domain, ADP-ribosylation factor
(ARF)-binding proteins (GGAs) facilitate distinct steps of post-Golgi
traffic. Human and yeast GGA proteins are only ~25% identical, but
all GGA proteins have four similar domains based on function and
sequence homology. GGA proteins are most conserved in the region that
interacts with ARF proteins. To analyze the role of ARF in GGA protein
localization and function, we performed mutational analyses of both
human and yeast GGAs. To our surprise, yeast and human GGAs differ in
their requirement for ARF interaction. We describe a point mutation in
both yeast and mammalian GGA proteins that eliminates binding to ARFs.
In mammalian cells, this mutation disrupts the localization of human
GGA proteins. Yeast Gga function was studied using an assay for
carboxypeptidase Y missorting and synthetic
temperature-sensitive lethality between GGAs and
VPS27. Based on these assays, we conclude that
non-Arf-binding yeast Gga mutants can function normally in membrane
trafficking. Using green fluorescent protein-tagged Gga1p, we show that
Arf interaction is not required for Gga localization to the Golgi.
Truncation analysis of Gga1p and Gga2p suggests that the N-terminal VHS
domain and C-terminal hinge and ear domains play significant roles in yeast Gga protein localization and function. Together, our data suggest
that yeast Gga proteins function to assemble a protein complex at the
late Golgi to initiate proper sorting and transport of specific cargo.
Whereas mammalian GGAs must interact with ARF to localize to and
function at the Golgi, interaction between yeast Ggas and Arf plays a
minor role in Gga localization and function.
Present address: Institute of Paper Science and
Technology, 500 10th St., N.W., Atlanta, GA 30318-5794.
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