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Molecular and Cellular Biology, December 2006, p. 8697-8709, Vol. 26, No. 23
0270-7306/06/$08.00+0 doi:10.1128/MCB.00708-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Specificity of Nuclear Import Substrates
The Max Delbrueck Center for Molecular Medicine, Robert Roessle Str. 10, 13125 Berlin, Germany,1 Institute of Biology, Center of Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany,2 Nephrology Section, Franz Volhard Clinic, HELIOS Klinikum Berlin, Wiltbergstr. 50, 13125 Berlin, Germany,3 Center for Nephrology and Hypertension, Ostsee Clinic and Reha Clinic Damp, Seute-Deern-Ring 30, 24351 Damp, Germany4
Received 25 April 2006/ Returned for modification 18 May 2006/ Accepted 18 September 2006
The "classical" nuclear protein import pathway depends on importin
and importin ß. Importin
binds nuclear localization signal (NLS)-bearing proteins and functions as an adapter to access the importin ß-dependent import pathway. In humans, only one importin ß is known to interact with importin
, while six
importins have been described. Various experimental approaches provided evidence that several substrates are transported specifically by particular
importins. Whether the NLS is sufficient to mediate importin
specificity is unclear. To address this question, we exchanged the NLSs of two well-characterized import substrates, the seven-bladed propeller protein RCC1, preferentially transported into the nucleus by importin
3, and the less specifically imported substrate nucleoplasmin. In vitro binding studies and nuclear import assays revealed that both NLS and protein context contribute to the specificity of importin
binding and transport.
Published ahead of print on 25 September 2006.
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