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Related Concept Videos

Nuclear Localization Signals and Import01:46

Nuclear Localization Signals and Import

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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...
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Nuclear Export01:42

Nuclear Export

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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.
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Regulation of Nuclear Protein Sorting01:45

Regulation of Nuclear Protein Sorting

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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...
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Regulated mRNA Transport02:22

Regulated mRNA Transport

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In eukaryotes, transcription and translation are compartmentalized; an mRNA is first synthesized in the nucleus and then selectively transported to the cytoplasm for protein synthesis. Before transport, a pre-mRNA undergoes several steps of post-transcriptional modifications including splicing, 5' capping, and the addition of a poly-adenine tail. Various proteins bind to the pre-mRNA during these modifications. The mRNA transport takes place with the help of multiple proteins playing...
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Nuclear Protein Sorting01:34

Nuclear Protein Sorting

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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...
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Leaky Scanning02:28

Leaky Scanning

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During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA.  Marilyn Kozak discovered that the sequence RCCAUGG (where R...
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Heterokaryon Technique for Analysis of Cell Type-specific Localization
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Sequence specificity of an essential nuclear localization sequence in Mcm3.

Ziyi Wang1,2, Yun Jing Zhang2, Qian-Yi Zhang1

  • 1Biomedical Science Graduate Program, University of California San Diego, San Diego, California, United States of America.

Plos Genetics
|January 21, 2025
PubMed
Summary

Nuclear localization sequences (NLSs) guide proteins into the cell nucleus. Precise positioning of basic residues in Mcm3

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Structural Biology

Background:

  • Proteins are directed to the cell nucleus via nuclear localization sequences (NLSs) that interact with importin proteins.
  • Identifying NLSs is challenging due to the absence of a universally conserved sequence, despite generally being short motifs rich in basic amino acids.

Purpose of the Study:

  • To characterize the sequence specificity of a conserved NLS in Mcm3, a subunit of the replicative DNA helicase.
  • To elucidate the structural basis of Mcm3 nuclear import and its dependence on importin interactions.

Main Methods:

  • Site-directed mutagenesis of the Mcm3 NLS.
  • AlphaFold 3 (AF3) modeling to predict protein structure and interactions.
  • Analysis of Mcm3 nuclear import, chromatin loading, and cell growth.

Main Results:

  • The precise positioning of basic amino acids within the Mcm3 NLS is critical for efficient nuclear import.
  • Disruption of NLS-importin interactions impairs Mcm3 nuclear import, leading to defective MCM complex chromatin loading.
  • Impaired nuclear import and chromatin loading of Mcm3 result in compromised cell growth.

Conclusions:

  • A structure-guided framework for predicting and analyzing monopartite NLSs was developed.
  • Key characteristics shared between Mcm3 and SV40 large T antigen NLSs were identified, despite sequence variability.
  • Understanding NLS sequence specificity is crucial for comprehending nuclear transport regulation and its impact on cellular function.