Related Experiment Video
Updated: Jun 17, 2026
08:53
Assay to Measure Nucleocytoplasmic Transport in Real Time within Motor Neuron-like NSC-34 Cells
Published on: May 16, 2017
Two isoforms of Npap60 (Nup50) differentially regulate nuclear protein import
Yutaka Ogawa1, Yoichi Miyamoto, Munehiro Asally
1Department of Frontier Biosciences, Graduate School of Frontier Biosciences, and Department of Biochemistry, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
Molecular Biology of the Cell
|December 18, 2009
Summary
Nuclear import in humans involves two Npap60 (Nup50) isoforms with opposing roles. Npap60S stabilizes cargo binding, while Npap60L promotes release, impacting nuclear protein transport efficiency.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Nuclear pore complexes regulate transport between the nucleus and cytoplasm.
- Nucleoporins, like Npap60 (Nup50), are key components of the nuclear pore.
- Npap60 interacts with importin alpha, a crucial protein for nuclear import.
Purpose of the Study:
- To investigate the distinct functions of the two human Npap60 isoforms (Npap60L and Npap60S) in nuclear protein import.
- To elucidate the mechanisms by which Npap60 isoforms modulate the importin alpha-cargo interaction.
- To determine the impact of Npap60 isoform levels on the efficiency of nuclear import.
Main Methods:
- In vitro binding assays to assess protein-protein interactions.
- Time-lapse microscopy experiments in vivo to observe nuclear import dynamics.
- Controlled manipulation of Npap60 protein levels.
Main Results:
- Npap60S stabilizes the interaction between importin alpha and nuclear localization signal (NLS)-containing cargo.
- Npap60L promotes the dissociation of NLS-cargo from importin alpha.
- Differential regulation of Npap60 isoform levels affects the rate of NLS-cargo nuclear import, with Npap60S suppressing and Npap60L accelerating import.
Conclusions:
- Npap60L and Npap60S exhibit opposing functions in nuclear protein import.
- The precise control of Npap60 isoform expression levels is critical for efficient nuclear import of classical NLS-cargo in humans.
- Nucleoporin expression levels represent a regulatory mechanism for nuclear import efficiency.
Related Concept Videos
01:45Regulation 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...
01:34Nuclear 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...
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...
01:46Nuclear 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...
01:42Nuclear 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...
NES are of three types- the canonical 10-residue long leucine-rich signal and other...
01:42Directionality 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...
02:31Nuclear 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...