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Related Concept Videos

Initiation of Translation02:33

Initiation of Translation

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Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
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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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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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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.
NES are of three types- the canonical 10-residue long leucine-rich signal and other...
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Nonsense-mediated mRNA Decay02:27

Nonsense-mediated mRNA Decay

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The Upf proteins that carry out nonsense-mediated decay (NMD) are found in all eukaryotic organisms, including humans. Each protein has an individual role, but they need to work in collaboration. Upf1 is an ATP-dependent RNA helicase that unwinds the RNA helix. Because Upf1 can unwind any RNA, Upf2 and Upf3 are required to help Upf1 discriminate between nonsense and normal mRNAs.
Usually, Upf3 binds to an Exon Junction Complex (EJC) at mRNA splice sites. If a ribosome fully translates the mRNA,...
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Nuclear Export of mRNA02:31

Nuclear Export of mRNA

7.6K
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: Jun 9, 2025

Monitoring eIF4F Assembly by Measuring eIF4E-eIF4G Interaction in Live Cells
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Nuclear release of eIF1 restricts start-codon selection during mitosis.

Jimmy Ly1,2, Kehui Xiang1,2,3, Kuan-Chung Su1,2

  • 1Whitehead Institute for Biomedical Research, Cambridge, MA, USA.

Nature
|October 24, 2024
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Summary

During mammalian mitosis, start codon selection becomes more stringent, altering protein production. This process, regulated by eIF1, is crucial for cell survival during mitotic stress.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • Regulated start-codon selection influences proteome diversity through alternative translation.
  • The precise conditions altering start-codon selection are not fully understood.
  • Mitosis involves significant cellular reorganization, potentially impacting translation.

Purpose of the Study:

  • To investigate global changes in start-codon selection during mammalian mitosis.
  • To identify the molecular mechanisms underlying altered translational control in mitosis.
  • To determine the physiological relevance of mitotic translational rewiring.

Main Methods:

  • Employed transcriptome-wide translation-initiation-site profiling to map translation start sites.
  • Analyzed ribosome association with eIF1 (eukaryotic initiation factor 1) during mitosis.
  • Utilized siRNA to deplete nuclear eIF1 and assessed its impact on translational stringency.

Main Results:

  • Revealed a global increase in start-codon selection stringency during mitosis.
  • Demonstrated that repressed low-efficiency initiation sites lead to widespread changes in protein isoforms.
  • Showed that enhanced stringency is mediated by increased 40S ribosome-eIF1 association, driven by nuclear eIF1 release.
  • Found that depleting nuclear eIF1 abrogates mitotic translational changes.
  • Observed increased cell death and reduced mitotic slippage when mitotic translational rewiring is prevented.

Conclusions:

  • Mammalian cells globally control translation initiation stringency during mitosis.
  • This regulation, involving eIF1 and ribosome interactions, is vital for preserving mitotic cell physiology.
  • Mitotic translational rewiring is essential for cell survival under stress, particularly during chemotherapy.