The auto-inhibitory function of importin alpha is essential in vivo

Proteins that contain a classical nuclear localization signal (NLS) are recognized in the cytoplasm by a heterodimeric import receptor composed of importin/karyopherin alpha and beta. The importin alpha subunit recognizes classical NLS sequences, and the importin beta subunit directs the complex to...

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Bibliographic Details
Published in:The Journal of biological chemistry 2003-02, Vol.278 (8), p.5854-5863
Main Authors: Harreman, Michelle T, Hodel, Mary R, Fanara, Patrizia, Hodel, Alec E, Corbett, Anita H
Format: Article
Language:English
Subjects:
alpha Karyopherins - antagonists & inhibitors
alpha Karyopherins - physiology
Amino Acid Sequence
Amino Acid Substitution
beta Karyopherins - physiology
Cell Nucleus - physiology
Humans
Models, Biological
Molecular Sequence Data
Protein Subunits - physiology
Recombinant Proteins - antagonists & inhibitors
Recombinant Proteins - metabolism
Saccharomyces cerevisiae
Saccharomyces cerevisiae - physiology
Sequence Alignment
Sequence Deletion
Sequence Homology, Amino Acid
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Summary:Proteins that contain a classical nuclear localization signal (NLS) are recognized in the cytoplasm by a heterodimeric import receptor composed of importin/karyopherin alpha and beta. The importin alpha subunit recognizes classical NLS sequences, and the importin beta subunit directs the complex to the nuclear pore. Recent work shows that the N-terminal importin beta binding (IBB) domain of importin alpha regulates NLS-cargo binding in the absence of importin beta in vitro. To analyze the in vivo functions of the IBB domain, we created a series of mutants in the Saccharomyces cerevisiae importin alpha protein. These mutants dissect the two functions of the N-terminal IBB domain, importin beta binding and auto-inhibition. One of these importin alpha mutations, A3, decreases auto-inhibitory function without impacting binding to importin beta or the importin alpha export receptor, Cse1p. We used this mutant to show that the auto-inhibitory function is essential in vivo and to provide evidence that this auto-inhibitory-defective importin alpha remains bound to NLS-cargo within the nucleus. We propose a model where the auto-inhibitory activity of importin alpha is required for NLS-cargo release and the subsequent Cse1p-dependent recycling of importin alpha to the cytoplasm.
ISSN:0021-9258
DOI:10.1074/jbc.M210951200