Importin
Encyclopedia
Importin is a type of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that moves other protein molecules into the nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 by binding to a specific recognition sequence, called the nuclear localization signal
Nuclear localization signal
A nuclear localization signal or sequence is an amino acid sequence which 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different...

 (NLS). Importin is classified as a karyopherin
Karyopherin
Karyopherins are a group of proteins involved in transporting molecules from the cytoplasm into the nucleus of eukaryotic cells. The inside of the nucleus is called the karyoplasm . Generally, karyopherin-mediated transport occurs through the nuclear pore, which acts as a gateway into and out of...

.

Importin has two subunits, importin α and importin β. Of these, importin α binds to the NLS of the protein to be imported to the nucleus whereas importin β helps in the docking of the importin heterodimer-bound protein to the nuclear pore complex. The NLS-Importin α-Importin β trimer dissociates after binding to Ran
Ran (biology)
Ran is a small 25Kda protein that is involved in transport into and out of the cell nucleus during interphase and also involved in mitosis. It is a member of the Ras superfamily....

 GTP inside the nucleus.

Human importin genes

  • Importin: , IPO7
    IPO7
    Importin-7 is a protein that in humans is encoded by the IPO7 gene.-Further reading:...

    , , IPO9
    IPO9
    Importin-9 is a protein that in humans is encoded by the IPO9 gene.-Further reading:...

    , ,
  • Karyopherin-α: KPNA1
    KPNA1
    Importin subunit alpha-1 is a protein that in humans is encoded by the KPNA1 gene.-Interactions:Karyopherin alpha 1 has been shown to interact with KPNB1 and UBR5.-Further reading:...

    , KPNA2
    KPNA2
    Importin subunit alpha-2 is a protein that in humans is encoded by the KPNA2 gene.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...

    , KPNA3
    KPNA3
    Importin subunit alpha-3 is a protein that in humans is encoded by the KPNA3 gene.-Further reading:...

    , KPNA4
    KPNA4
    Importin subunit alpha-4 is a protein that in humans is encoded by the KPNA4 gene.-Further reading:...

    , KPNA5
    KPNA5
    Importin subunit alpha-6 is a protein that in humans is encoded by the KPNA5 gene.-Further reading:...

    , KPNA6
    KPNA6
    Importin subunit alpha-7 is a protein that in humans is encoded by the KPNA6 gene.-Further reading:...

  • Karyopherin-β: KPNB1
    KPNB1
    Importin subunit beta-1 is a protein that in humans is encoded by the KPNB1 gene.-Interactions:KPNB1 has been shown to interact with NUP98, Karyopherin alpha 1, KPNA3, Karyopherin alpha 2, SMN1, Parathyroid hormone-related protein, Nucleoporin 62, RANBP2, Ran , RANBP1, NUP50, P53, NUP153 and...

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