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* Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115; The short filaments extending from the cytoplasmic face of nuclear pore complexes are thought to
contain docking sites for nuclear import substrates.
One component of these filaments is the large O-linked
glycoprotein CAN/Nup214. Immunoprecipitation studies carried out under nondenaturing conditions, and using a variety of antibodies, reveal a novel nonglycosylated nucleoporin, Nup84, that is tightly associated with
CAN/Nup214. Consistent with such an association,
Nup84 is found to be exposed on the cytoplasmic face
of the nuclear pore complex. cDNA sequence analyses indicate that Nup84 contains neither the GLFG nor the
XFXFG repeats that are a characteristic of a number of
other nuclear pore complex proteins. Secondary structure predictions, however, suggest that Nup84 contains
a coiled-coil COOH-terminal domain, a conclusion supported by the observation of significant sequence
similarity between this region of the molecule and various members of the tropomyosin family. Mutagenesis
and expression studies indicate that the putative
coiled-coil domain is required for association with the
cytoplasmic face of the nuclear pore complex, whereas it is the NH2-terminal region of Nup84 that contains the
site of interaction with CAN/Nup214. These findings
suggest a model in which Nup84 may function in the attachment of CAN/Nup214 to the central framework of
the nuclear pore complex. In this way, Nup84 could
play a central role in the organization of the interface between the pore complex and the cytoplasm.
Faculty of Medicine, University of
Calgary, Calgary, Alberta T2N 4N1, Canada; and § Department of Biology, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139
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