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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...

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...

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...

Protein Transport into the Inner Mitochondrial Membrane

Protein Transport into the Inner Mitochondrial Membrane

Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...

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Related Experiment Video

Updated: Jul 7, 2026

Single-Molecule Imaging of Nuclear Transport

Single-Molecule Imaging of Nuclear Transport

Published on: June 9, 2010

Nuclear import in digitonin-permeabilized cells.

M S Moore¹, E D Schwoebel

¹Baylor College of Medicine, Houston, Texas, USA.

Current Protocols in Cell Biology

|January 30, 2008

Summary

This summary is machine-generated.

Nuclear protein import can be studied in a cell-free system using Xenopus egg extracts. This method reconstitutes nuclear import and helps identify nuclear localization sequences (NLS).

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Last Updated: Jul 7, 2026

Single-Molecule Imaging of Nuclear Transport

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Published on: June 9, 2010

Cholinergic Ligand–dependent Modulation of Oxidative Phosphorylation Coupling in Digitonin-permeabilized BE(2)-C Neuroblastoma Cells

Cholinergic Ligand–dependent Modulation of Oxidative Phosphorylation Coupling in Digitonin-permeabilized BE(2)-C Neuroblastoma Cells

Published on: April 28, 2026

Area of Science:

Cell Biology
Molecular Biology
Biochemistry

Background:

Nuclear protein import is essential for cellular function.
This complex process requires cytosolic factors and specific nuclear signals.
Previous methods for studying nuclear import were limited.

Purpose of the Study:

To establish an in vitro system for studying nuclear protein import.
To identify the cytosolic factors involved in nuclear import.
To characterize nuclear localization sequences (NLS).

Main Methods:

Utilized digitonin-permeabilized cells to create competent nuclei.
Employed Xenopus ovarian cell extracts to supply necessary cytosolic factors.
Visualized nuclear import using fluorochrome-conjugated probes, GFP-tagged proteins, and antibodies.

Main Results:

Successfully reconstituted the nuclear import process in vitro.
Demonstrated the system's ability to support the import of various protein probes.
Showcased the utility of the system in identifying nuclear localization sequences (NLS).

Conclusions:

The developed in vitro system accurately reflects the in vivo nuclear import process.
This system provides a valuable tool for dissecting the molecular mechanisms of nuclear transport.
The system facilitates the identification and characterization of nuclear localization signals.