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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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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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Improving Translational Accuracy02:07

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Base complementarity between the three base pairs of mRNA codon and the tRNA anticodon is not a failsafe mechanism. Inaccuracies can range from a single mismatch to no correct base pairing at all. The free energy difference between the correct and nearly correct base pairs can be as small as 3 kcal/ mol. With complementarity being the only proofreading step, the estimated error frequency would be one wrong amino acid in every 100 amino acids incorporated. However, error frequencies observed in...
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Directing Proteins to the Rough Endoplasmic Reticulum01:34

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The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. Some of the proteins directed to ER are then trafficked via vesicles to other organelles within the cell or the extracellular environment through the Golgi complex. For example, the rough ER synthesizes soluble proteins for transportation to the lysosomes or secretion out of the cell. It can also synthesize transmembrane proteins that can...
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Nonsense-mediated mRNA Decay02:27

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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.
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Monitoring eIF4F Assembly by Measuring eIF4E-eIF4G Interaction in Live Cells
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eIF3 Peripheral Subunits Rearrangement after mRNA Binding and Start-Codon Recognition.

Angelita Simonetti1, Jailson Brito Querido1, Alexander G Myasnikov2

  • 1CNRS, Architecture et Réactivité de l'ARN UPR9002, Université de Strasbourg, 67084 Strasbourg, France.

Molecular Cell
|July 5, 2016
PubMed
Summary

Eukaryotic translation initiation involves eukaryotic initiation factors (eIFs). This study reveals the structural rearrangement of the eIF3 complex during mRNA scanning and ribosomal subunit joining.

Keywords:
cryo-EMeIF3eIF3 peripheral subunitseukaryotic translation initiationribosome

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Biochemistry

Background:

  • mRNA translation initiation is a complex process in eukaryotes.
  • It requires multiple eukaryotic initiation factors (eIFs) to form functional complexes.
  • The eukaryotic initiation factor 3 (eIF3) complex, with 13 subunits, is crucial for mRNA binding and start codon recognition.

Purpose of the Study:

  • To elucidate the structural dynamics of the eIF3 complex during mRNA translation initiation.
  • To understand the molecular mechanisms of eIF3 in mRNA scanning and ribosomal subunit joining.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was used to determine the structure of a mammalian 48S initiation complex.
  • High-resolution structural analysis was performed at 5.8 Å.

Main Results:

  • The study revealed the relocation of eIF3 subunits (eIF3i and eIF3g) to the 40S ribosomal subunit's intersubunit face.
  • Relocation of eIF3b was observed, binding below the eIF2-Met-tRNAi(Met) ternary complex.
  • Deep rearrangements within the eIF3 complex were identified during late-stage initiation.

Conclusions:

  • The findings provide insights into the dynamic structural changes of eIF3 during translation initiation.
  • This work unravels the molecular basis of eIF3's role in mRNA scanning and the timing of ribosomal subunit joining.