Distinct functions for the two importin subunits in nuclear protein import

Dirk Görlich*, Frank Vogel, Anthony D. Mills, Enno Hartmann, Ronald A. Laskey

*Corresponding author for this work
382 Citations (Scopus)


THE import of nuclear proteins proceeds through the nuclear pore complex and requires nuclear localization signals (NLSs)1,2, energy 3,4 and soluble factors5, namely importin-α(M r 60K)6-12,28, importin-β (90K)8-11,13 and Ran14,15. Importin-α is primarily responsible for NLS recognition6-12,29 and is a member of a protein family that includes the essential yeast nuclear pore protein SRPlp (ref. 16). As the first event, the complex of importin-α and importin-β binds the import substrate in the cytosol8,9. Here we show that this nuclear pore targeting complex initially docks as a single entity to the nuclear pore via importin-β. Then the energy-dependent, Ran-mediated translocation through the pore results in the accumulation of import substrate and importin-α in the nucleus. In contrast, importin-β accumulates at the nuclear envelope, but not in the nucleoplasm. Immunoelectron microscopy detects importin-β on both sides of the nuclear pore. This suggests that the nuclear pore targeting complex might move as a single entity from its initial docking site through the central part of the nuclear pore before it disassembles on the nucleoplasmic side.

Original languageEnglish
Issue number6546
Pages (from-to)246-248
Number of pages3
Publication statusPublished - 01.12.1995


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