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J. Cell Biol.,
Volume 142, Number 3, August 10, 1998 665-681
Division of Cellular and Molecular Medicine and Howard Hughes Medical Institute, University of California at San Diego,
School of Medicine, La Jolla, California 92093-0668
We have recently characterized three yeast
gene products (Vps35p, Vps29p, and Vps30p) as candidate components of the sorting machinery required for
the endosome-to-Golgi retrieval of the vacuolar protein sorting receptor Vps10p (Seaman, M.N.J., E.G. Marcusson, J.-L. Cereghino, and S.D. Emr. 1997. J. Cell
Biol. 137:79-92). By genetic and biochemical means we
now show that Vps35p and Vps29p interact and form
part of a multimeric membrane-associated complex
that also contains Vps26p, Vps17p, and Vps5p. This
complex, designated here as the retromer complex, assembles from two distinct subcomplexes comprising (a)
Vps35p, Vps29p, and Vps26p; and (b) Vps5p and
Vps17p. Density gradient fractionation of Golgi/endosomal/vesicular membranes reveals that Vps35p cofractionates with Vps5p/Vps17p in a vesicle-enriched dense
membrane fraction. Furthermore, gel filtration analysis
indicates that Vps35p and Vps5p are present on a population of vesicles and tubules slightly larger than
COPI/coatomer-coated vesicles. We also show by immunogold EM that Vps5p is localized to discrete regions at the rims of the prevacuolar endosome where vesicles appear to be budding. Size fractionation of cytosolic and recombinant Vps5p reveals that Vps5p can
self-assemble in vitro, suggesting that Vps5p may provide the mechanical impetus to drive vesicle formation.
Based on these findings we propose a model in which
Vps35p/Vps29p/Vps26p function to select cargo for retrieval, and Vps5p/Vps17p assemble onto the membrane to promote vesicle formation. Conservation of
the yeast retromer complex components in higher eukaryotes suggests an important general role for this
complex in endosome-to-Golgi retrieval.
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