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J. Cell Biol.,
Volume 144, Number 4, February 22, 1999 645-655
Department of Anatomy and Cell Biology, Osaka University Medical School, Suita, Osaka 565-0871, Japan
A small GTPase Ran is a key regulator for
active nuclear transport. In immunoblotting analysis, a
monoclonal antibody against recombinant human Ran,
designated ARAN1, was found to recognize an epitope
in the COOH-terminal domain of Ran. In a solution
binding assay, ARAN1 recognized Ran when complexed with importin 
, transportin, and CAS, but not
the Ran-GTP or the Ran-GDP alone, indicating that
the COOH-terminal domain of Ran is exposed via its
interaction with importin -related proteins. In addition, ARAN1 suppressed the binding of RanBP1 to the
Ran-importin complex. When injected into the nucleus of BHK cells, ARAN1 was rapidly exported
to the cytoplasm, indicating that the Ran-importin
-related protein complex is exported as a complex
from the nucleus to the cytoplasm in living cells. Moreover, ARAN1, when injected into the cultured cells induces the accumulation of endogenous Ran in the
cytoplasm and prevents the nuclear import of SV-40
T-antigen nuclear localization signal substrates. From
these findings, we propose that the binding of RanBP1
to the Ran-importin complex is required for the dissociation of the complex in the cytoplasm and that the
released Ran is recycled to the nucleus, which is essential for the nuclear protein transport.
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