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J. Cell Biol.,
Volume 145, Number 6, June 14, 1999 1189-1198

* Division of Cellular and Molecular Medicine, University of California, San Diego, San Diego, California 92093; By using an immunoisolation procedure
(Stan, R.-V., W.G. Roberts, K. Ihida, D. Predescu, L. Saucan, L. Ghitescu, and G.E. Palade. 1997. Mol. Biol.
Cell. 8:595-605) developed in our laboratory, we have
isolated a caveolar subfraction from rat lung endothelium and we have partially characterized the proteins of
this subfraction which include an apparently caveolae-specific glycoprotein we propose to call PV-1 (formerly
known as gp68). The isolation and partial sequencing of
PV-1, combined with the cloning of the full length PV-1
cDNA led to the following conclusions: (a) PV-1 is a
novel single span type II integral membrane protein
(438 amino acids long) which forms homodimers in situ;
(b) the transmembrane domain of PV-1 is near the NH2
terminus defining a short cytoplasmic endodomain and
a large COOH-terminal ectodomain exposed to the blood plasma; (c) PV-1 is N-glycosylated and its glycan
antennae bear terminal nonreducing galactosyl residues in
Department of
Pathology and Cell Biology, University of Montreal, Montreal, Canada H3C 1J4; and § Department of Biochemistry and Cell
Biology, University of Massachusetts, Amherst, Massachusetts 01003
1-3 linkage. PV-1 is expressed mostly in the
lung but both the messenger RNA and the protein can
be detected at lower levels also in kidney, spleen, liver,
heart, muscle, and brain. No signal could be detected in
testis and two lower molecular weight forms were detected in brain. Immunocytochemical studies carried
out by immunodiffusion on rat lung with an anti-PV-1
polyclonal antibody directed against a COOH-terminal
epitope reveal a specific localization of PV-1 to the stomatal diaphragms of rat lung endothelial caveolae and confirm the extracellular orientation of the PV-1
COOH terminus.
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