Transportin acts to regulate mitotic assembly events by target binding rather than Ran sequestration
| Autor: | Yuh Min Chook, Douglass J. Forbes, Sarah Carmona, Beth Swift-Taylor, Cyril Bernis, Matthew S Nord |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2014 |
| Předmět: |
Cell Extracts
Nuclear Envelope Xenopus Molecular Sequence Data Nuclear Localization Signals Mitosis Importin Spindle Apparatus Biology Karyopherins Xenopus Proteins Models Biological 03 medical and health sciences 0302 clinical medicine Animals Drosophila Proteins Humans Amino Acid Sequence Kinetochores Molecular Biology Interphase 030304 developmental biology Cytokinesis 0303 health sciences Kinetochore Cell Cycle Cell Biology Articles beta Karyopherins Chromatin Spindle apparatus Cell biology Nuclear Pore Complex Proteins ran GTP-Binding Protein Ran Beta Karyopherins Mutant Proteins Peptides 030217 neurology & neurosurgery HeLa Cells Protein Binding |
| Zdroj: | Molecular Biology of the Cell |
| ISSN: | 1939-4586 1059-1524 |
| Popis: | Transportin-specific molecular tools are used to show that the mitotic cell contains importin β and transportin “global positioning system” pathways that are mechanistically parallel. Transportin works to control where the spindle, nuclear membrane, and nuclear pores are formed by directly affecting assembly factor function. The nuclear import receptors importin β and transportin play a different role in mitosis: both act phenotypically as spatial regulators to ensure that mitotic spindle, nuclear membrane, and nuclear pore assembly occur exclusively around chromatin. Importin β is known to act by repressing assembly factors in regions distant from chromatin, whereas RanGTP produced on chromatin frees factors from importin β for localized assembly. The mechanism of transportin regulation was unknown. Diametrically opposed models for transportin action are as follows: 1) indirect action by RanGTP sequestration, thus down-regulating release of assembly factors from importin β, and 2) direct action by transportin binding and inhibiting assembly factors. Experiments in Xenopus assembly extracts with M9M, a superaffinity nuclear localization sequence that displaces cargoes bound by transportin, or TLB, a mutant transportin that can bind cargo and RanGTP simultaneously, support direct inhibition. Consistently, simple addition of M9M to mitotic cytosol induces microtubule aster assembly. ELYS and the nucleoporin 107–160 complex, components of mitotic kinetochores and nuclear pores, are blocked from binding to kinetochores in vitro by transportin, a block reversible by M9M. In vivo, 30% of M9M-transfected cells have spindle/cytokinesis defects. We conclude that the cell contains importin β and transportin “global positioning system”or “GPS” pathways that are mechanistically parallel. |
| Databáze: | OpenAIRE |
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