Nuclear localization signal and protein context both mediate importin alpha specificity of nuclear import substrates.
The "classical" nuclear protein import pathway depends on importin alpha and importin beta. Importin alpha binds nuclear localization signal (NLS)-bearing proteins and functions as an adapter to access the importin beta-dependent import pathway. In humans, only one importin beta is known to interact with importin alpha, while six alpha importins have been described. Various experimental approaches provided evidence that several substrates are transported specifically by particular alpha importins. Whether the NLS is sufficient to mediate importin alpha 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 alpha3, 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 alpha binding and transport.
Friedrich
Beate
B
The Max Delbrueck Center for Molecular Medicine, Robert Roessle Strasse 10, 13125 Berlin, Germany.
Quensel
Christina
C
Sommer
Thomas
T
Hartmann
Enno
E
Köhler
Matthias
M
D021581:Active Transport, Cell Nucleus; D001692:Biological Transport; D018797:Cell Cycle Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005982:Glutathione Transferase / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019913:Nuclear Localization Signals / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D056489:Nucleoplasmins; D010750:Phosphoproteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D013379:Substrate Specificity; D028901:alpha Karyopherins / Q000235:genetics / Q000378:metabolism*
D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D056489:Nucleoplasmins; D010750:Phosphoproteins; D011506:Proteins; C062521:RCC1 protein, human; D011993:Recombinant Fusion Proteins; D028901:alpha Karyopherins; D005982:Glutathione Transferase