Related Experiment Video

Updated: Aug 19, 2026

Heterokaryon Technique for Analysis of Cell Type-specific Localization
09:31

Heterokaryon Technique for Analysis of Cell Type-specific Localization

Published on: March 11, 2011

Characterization of the nuclear import of human MutLalpha

A Brieger1, G Plotz, J Raedle

  • 1Medizinische Klinik I, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt a.M., Germany.

Molecular Carcinogenesis
|March 9, 2005
PubMed

Insights

DNA mismatch repair (MMR) maintains DNA replication accuracy. Nuclear localization signals (NLS) in hMLH1 and hPMS2 regulate MMR protein import, with mutations impairing this crucial nuclear transport.

Area of Science:

  • Molecular Biology
  • Genetics
  • Cell Biology

Background:

  • DNA mismatch repair (MMR) is critical for genomic stability and replication fidelity.
  • The precise regulation of MMR protein nuclear import remains poorly understood.
  • Nuclear localization signals (NLS) are key for protein transport into the nucleus.

Purpose of the Study:

  • To investigate the role of potential nuclear localization signals (NLS) in the human MMR proteins hMLH1 and hPMS2.
  • To determine how mutations in candidate NLS sequences affect the nuclear import of hMLH1 and hPMS2.

Main Methods:

  • Generation of NLS mutants for hMLH1 and hPMS2.
  • Expression of wild-type and mutant proteins in 293T cells.
  • Confocal laser microscopy to analyze subcellular localization.

Main Results:

  • Identified candidate NLS sequences in hMLH1 (aa 469-472, 496-499) and hPMS2 (aa 574-580).
  • Demonstrated that mutations in specific NLS sequences impair nuclear import of hMLH1 and hPMS2.
  • Observed significant nuclear import defects for hMLH1 mutants (K471, R472) and hPMS2 mutants (K577, R578).

Conclusions:

  • Specific NLS sequences in hMLH1 and hPMS2 are essential for their nuclear import.
  • Nuclear import regulation is a key mechanism controlling MMR protein function.
  • Mutations affecting NLS can disrupt DNA mismatch repair by impairing nuclear localization.

Related Concept Videos

Nuclear Localization Signals and Import01:46

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 Sorting01:34

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 Export01:42

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...
Regulation of Nuclear Protein Sorting01:45

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 mRNA02:31

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...
Nuclear Export of mRNA02:31

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...