The import of proteins into the nucleus is a process that involves at least 2 steps. The first is an energy-independent docking of the protein to the nuclear envelope and the second is an energy-dependent translocation through the nuclear pore complex. Imported proteins require a nuclear localization sequence (NLS) which generally consists of a short region of basic amino acids or 2 such regions spaced about 10 amino acids apart. Proteins involved in the first step of nuclear import have been identified in different systems. These include the Xenopus protein importin and its yeast homolog, SRP1 (a suppressor of certain temperature-sensitive mutations of RNA polymerase I in Saccharomyces cerevisiae), which bind to the NLS. KPNA2 protein interacts with the NLSs of DNA helicase Q1 and SV40 T antigen and may be involved in the nuclear transport of proteins. KPNA2 also may play a role in V(D)J recombination [provided by RefSeq, Jul 2008]
Function:
Functions in nuclear protein import as an adapter protein for nuclear receptor KPNB1. Binds specifically and directly to substrates containing either a simple or bipartite NLS motif. Docking of the importin/substrate complex to the nuclear pore complex (NPC) is mediated by KPNB1 through binding to nucleoporin FxFG repeats and the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin-beta and the three components separate and importin-alpha and -beta are re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran from importin. The directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus.
Subcellular Location:
Cytoplasm. Nucleus.
Tissue Specificity:
Expressed ubiquitously.
Similarity:
Belongs to the importin alpha family.
Contains 10 ARM repeats.
Contains 1 IBB domain.
SWISS:
P52292
Gene ID:
3838
Database links:
Entrez Gene: 3838 Human
Entrez Gene: 100039592 Mouse
Entrez Gene: 100043906 Mouse
Entrez Gene: 16647 Mouse
Omim: 600685 Human
SwissProt: P52292 Human
SwissProt: P52293 Mouse
Unigene: 594238 Human
Unigene: 12508 Mouse
Unigene: 391577 Mouse
Unigene: 423000 Mouse
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