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Nuclear Export

Nuclear Export

The nucleus restricts several proteins within and allows others to pass. The restricted proteins possess a nuclear retention sequence or NRS, anchoring them to the nuclear lamins and preventing their transport to the cytosol. The non-restricted proteins, after their synthesis, are transported to their site of action, such as the cytosol or other organelles, with the help of nuclear export signals or NES.
NES are of three types- the canonical 10-residue long leucine-rich signal and other...

Nuclear Localization Signals and Import

Nuclear Localization Signals and Import

Proteins targeted to the nucleus carry short stretches of amino acid sequences called the nuclear localization signal or NLS. Classical nuclear localization signals are of two types: monopartite and bipartite NLS. Monopartite classical NLS (cNLS) consists of a single cluster of 4-8 amino acids. Bipartite cNLS consists of two clusters of 2-3 amino acids and a 9-12 residue long proline-rich linker bridging the two clusters. Signal clusters are rich in positively charged amino acids such as...

Nuclear Protein Sorting

Nuclear Protein Sorting

Nuclear protein sorting is the selective trafficking of histones, polymerases, gene regulatory proteins into the nucleus and exporting RNAs and ribosomes to the cytosol. It is a tightly controlled process that regulates gene expression within a cell.
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...

Directionality of Nuclear Transport

Directionality of Nuclear Transport

Ras-related nuclear protein or Ran is a small G protein that cycles between its GTP and GDP bound states. Ran specific regulators, a Ran GTPase Activating Protein or RanGAP present in the cytosol and a Ran guanine nucleotide exchange factor or RanGEF present inside the nucleus regulate GTP/GDP exchange. A high concentration of GTP inside the cells, in addition to this asymmetric distribution of Ran-specific regulators, leads to a higher RanGTP concentration inside the nucleus. This...

Regulation of Nuclear Protein Sorting

Regulation of Nuclear Protein Sorting

Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...

Nuclear Export of mRNA

Nuclear Export of mRNA

Before mRNAs are exported to the cytoplasm, it is crucial to check each mRNA for structural and functional integrity. Eukaryotic cells use several different mechanisms, collectively known as mRNA surveillance, to look for irregularities in mRNAs. Irregular or aberrant mRNA are rapidly degraded by various enzymes. If a defective mRNA escapes the surveillance, it would be translated into a protein which would either be non-functional or not function properly. One of the primary irregularities in...

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Related Experiment Video

Updated: May 13, 2026

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection

Published on: December 4, 2010

Structural basis for the nuclear export activity of Importin13.

Marlene Grünwald¹, Daniela Lazzaretti, Fulvia Bono

¹Max Planck Institute for Developmental Biology, Tübingen, Germany.

The EMBO Journal

|February 26, 2013

Summary

Importin13 (Imp13) is a bidirectional karyopherin. Structural studies reveal how Imp13 exports translation initiation factor 1A (eIF1A) by binding it to its C-terminal arch, essential for cellular function.

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Last Updated: May 13, 2026

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection

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Published on: December 4, 2010

Single-Molecule Imaging of Nuclear Transport

Single-Molecule Imaging of Nuclear Transport

Published on: June 9, 2010

Area of Science:

Cell Biology
Molecular Biology
Structural Biology

Background:

Importin13 (Imp13) functions as a bidirectional karyopherin, mediating both the import and export of cellular cargoes.
Imp13 interacts with import cargoes like Mago-Y14 and Ubc9, and the export cargo translation initiation factor 1A (eIF1A).

Purpose of the Study:

To elucidate the molecular mechanism by which Importin13 (Imp13) performs its dual role in cargo transport.
To understand how Imp13 facilitates the export of translation initiation factor 1A (eIF1A).

Main Methods:

Determined crystal structures of Imp13 in complex with RanGTP and eIF1A at 3.6 Å resolution.
Obtained a 3.0 Å crystal structure of unbound Imp13 to reveal its conformational states.
Performed in vivo experiments to validate Imp13's binding and export capabilities for eIF1A.

Main Results:

The crystal structure shows eIF1A binding to the inner surface of the Imp13 C-terminal arch, adjacent to RanGTP, explaining export mechanism.
The unbound Imp13 structure reveals an open conformation, crucial for releasing export cargoes in the cytoplasm.
Demonstrated that Imp13 binds and exports eIF1A in vivo, confirming its essential role in this process.

Conclusions:

Imp13's ability to bind both import and export cargoes is structurally explained.
The open conformation of Imp13 is key to releasing export cargoes, completing the export pathway.
Imp13 plays an essential, functionally validated role in the export of eIF1A.