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* Department of Biochemistry, Here, we report the localization and characterization of BHKp23, a member of the p24 family of
transmembrane proteins, in mammalian cells. We find
that p23 is a major component of tubulovesicular membranes at the cis side of the Golgi complex (estimated
density: 12,500 copies/µm2 membrane surface area, or
Department of Cell Biology, University of Geneva, 1211 Geneva 4, Switzerland; § Institute of
Physiological Chemistry and Patobiochemistry, Gutenberg Universität, 55099 Mainz, Germany; and
Centre for Microscopy and
Microanalysis, Department of Physiology and Pharmacology, and Centre for Molecular and Cellular Biology, University of
Queensland, Queensland 4072, Brisbane, Australia
30% of the total protein). Our data indicate that
BHKp23-containing membranes are part of the cis-Golgi network/intermediate compartment . Using the
G protein of vesicular stomatitis virus as a transmembrane cargo molecule, we find that p23 membranes are
an obligatory station in forward biosynthetic membrane transport, but that p23 itself is absent from transport vesicles that carry the G protein to and beyond the
Golgi complex. Our data show that p23 is not present to
any significant extent in coat protein (COP) I-coated
vesicles generated in vitro and does not colocalize with
COP I buds and vesicles. Moreover, we find that p23
cytoplasmic domain is not involved in COP I membrane recruitment. Our data demonstrate that microinjected antibodies against the cytoplasmic tail of p23 inhibit G protein transport from the cis-Golgi network/
intermediate compartment to the cell surface, suggesting that p23 function is required for the transport of
transmembrane cargo molecules. These observations
together with the fact that p23 is a highly abundant
component in the intermediate compartment, lead us to
propose that p23 contributes to membrane structure,
and that this contribution is necessary for efficient segregation and transport.
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