Related Experiment Video
Updated: May 3, 2026

Single-Molecule Imaging of Nuclear Transport
Published on: June 10, 2010
Export of importin alpha from the nucleus is mediated by a specific nuclear transport factor
U Kutay1, F R Bischoff, S Kostka
1Zentrum für Molekulare Biologie der Universität Heidelberg, Federal Republic of Germany.
Abstract:
NLS proteins are transported into the nucleus by the importin alpha/beta heterodimer. Importin alpha binds the NLS, while importin beta mediates translocation through the nuclear pore complex. After translocation, RanGTP, whose predicted concentration is high in the nucleus and low in the cytoplasm, binds importin beta and displaces importin alpha. Importin alpha must then be returned to the cytoplasm, leaving the NLS protein behind. Here, we report that the previously identified CAS protein mediates importin alpha re-export. CAS binds strongly to importin alpha only in the presence of RanGTP, forming an importin alpha/CAS/RanGTP complex. Importin alpha is released from this complex in the cytoplasm by the combined action of RanBP1 and RanGAP1. CAS binds preferentially to NLS-free importin alpha, explaining why import substrates stay in the nucleus.
Related Concept Videos
Nuclear Export of mRNA
Nuclear Protein Sorting
Proteins targeted to the nucleus carry nuclear localization signals or NLS recognized by import receptors in the cytosol. Similarly, proteins with nuclear export signals are recognized by export receptors. Import and export receptors are...
Nuclear Localization Signals and Import
Nuclear Export
NES are of three types- the canonical 10-residue long leucine-rich signal and other...
Directionality of Nuclear Transport
Regulation of Nuclear Protein Sorting

