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J. Cell Biol.,
Volume 141, Number 7, June 29, 1998 1515-1527
Division of Cellular and Molecular Medicine and Department of Pathology, University of California, San Diego, La Jolla,
California 92093-0651
We have identified CALNUC, an EF-hand,
Ca2+-binding protein, as a Golgi resident protein.
CALNUC corresponds to a previously identified EF-hand/calcium-binding protein known as nucleobindin. CALNUC interacts with G
i3 subunits in the yeast two-hybrid system and in GST-CALNUC pull-down assays.
Analysis of deletion mutants demonstrated that the
EF-hand and intervening acidic regions are the site of
CALNUC's interaction with G
i3. CALNUC is found
in both cytosolic and membrane fractions. The membrane pool is tightly associated with the luminal surface
of Golgi membranes. CALNUC is widely expressed, as
it is detected by immunofluorescence in the Golgi region of all tissues and cell lines examined. By immunoelectron microscopy, CALNUC is localized to cis-Golgi
cisternae and the cis-Golgi network (CGN). CALNUC
is the major Ca2+-binding protein detected by 45Ca2+-binding assay on Golgi fractions. The properties of
CALNUC and its high homology to calreticulin suggest
that it may play a key role in calcium homeostasis in the
CGN and cis-Golgi cisternae.
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