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J. Cell Biol.,
Volume 140, Number 4, February 23, 1998 751-765
* Department of Anatomy and Cell Biology, McGill University, Montreal, PQ, H3A2B2, Canada; Abstract. Five mammalian members of the gp25L/
emp24/p24 family have been identified as major constituents of the cis-Golgi network of rat liver and HeLa
cells. Two of these were also found in membranes of
higher density (corresponding to the ER), and this correlated with their ability to bind COP I in vitro. This binding was mediated by a K(X)KXX-like retrieval
motif present in the cytoplasmic domain of these two
members. A second motif, double phenylalanine (FF),
present in the cytoplasmic domain of all five members,
was shown to participate in the binding of Sec23 (COP
II). This motif is part of a larger one, similar to the
F/YXXXXF/Y strong endocytosis and putative AP2
binding motif. In vivo mutational analysis confirmed
the roles of both motifs so that when COP I binding
was expected to be impaired, cell surface expression
was observed, whereas mutation of the Sec23 binding
motif resulted in a redistribution to the ER. Surprisingly, upon expression of mutated members, steady-state distribution of unmutated ones shifted as well,
presumably as a consequence of their observed oligomeric properties.
Cell Biology Programme,
European Molecular Biology Laboratory, 69012 Heidelberg, Germany; Genetics Group, Biotechnology Research Institute,
National Research Council of Canada, H4P2R2 Montreal, Canada; and § Department of Morphology, University of Geneva
School of Medicine, 4CH-1211 Geneva, Switzerland
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