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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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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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Ribosomal RNA Synthesis02:53

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Ribosome synthesis is a highly complex and coordinated process involving more than 200 assembly factors. The synthesis and processing of ribosomal components occurs not only in the nucleolus but also in the nucleoplasm and the cytoplasm of eukaryotic cells.
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Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.  Most protein complexes self-assemble spontaneously via ordered pathways, while some proteins need assembly factors that guide their proper assembly. Despite the crowded intracellular environment, proteins usually interact with their correct partners and form functional complexes.
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Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of hemoglobin, is present in all cells of the body. However, it is only expressed in red blood cells because the transcription factors that can bind to the promoter sequences of the beta globin gene are only expressed in these cells. Tissue-specific transcription factors also ensure that mutations in these factors may impair only the function of...
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Translation in Prokaryotes01:29

Translation in Prokaryotes

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Prokaryote translation is a complex, highly coordinated process that converts genetic information from mRNA into functional proteins. It involves three stages: initiation, elongation, and termination, each facilitated by specific molecular components.Initiation of TranslationThe process begins with the assembly of the ribosomal subunits and initiation factors on the mRNA. In bacteria, the 30S ribosomal subunit recognizes the Shine-Dalgarno sequence in the mRNA, a conserved region upstream of...
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Related Experiment Video

Updated: Oct 6, 2025

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs
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Stepwise assembly of the eukaryotic translation initiation factor 2 complex.

Sven Vanselow1, Lea Neumann-Arnold1, Franziska Wojciech-Moock1

  • 1Department of Genetics, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany.

The Journal of Biological Chemistry
|January 15, 2022
PubMed
Summary

The eukaryotic translation initiation factor 2 (eIF2) assembly mechanism was clarified using yeast models. A new model shows how subunits eIF2α and eIF2β bind independently to eIF2γ, with eIF2α completing assembly.

Keywords:
Cdc123cell proliferationeukaryotic initiation factor 2human eIF2molecular chaperoneprotein assemblyprotein complexprotein–protein interactiontranslation initiation factoryeast

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The eukaryotic translation initiation factor 2 (eIF2) is crucial for protein synthesis initiation.
  • eIF2 function is vital for cellular response to stress and its dysfunction is linked to neurological diseases.
  • The precise assembly mechanism and subunit roles within the eIF2 complex were previously unclear.

Purpose of the Study:

  • To elucidate the detailed assembly mechanism of the eukaryotic translation initiation factor 2 (eIF2) complex.
  • To investigate the roles and interactions of eIF2 subunits (eIF2α, eIF2β, eIF2γ) during complex formation.
  • To determine the involvement of Cdc123 in the eIF2 assembly process.

Main Methods:

  • Quantitative analysis of assembly intermediates in budding yeast.
  • Site-directed mutagenesis to study binding site mutant behaviors.
  • Experiments in human cell culture to assess cross-species conservation.

Main Results:

  • A model was proposed where Cdc123 induces a conformational change in eIF2γ, exposing binding sites for eIF2α and eIF2β.
  • eIF2α and eIF2β binding to eIF2γ are independent, forming nonfunctional heterodimers that do not bind eIF2B.
  • eIF2α levels impact assembly rate, and its binding to eIF2γ displaces Cdc123, completing assembly.

Conclusions:

  • The study presents a novel model for eIF2 complex assembly, detailing subunit interactions and the role of Cdc123.
  • The findings reveal that eIF2α binding is the final step in eIF2 assembly, displacing Cdc123.
  • The conserved nature of this mechanism across yeast and human cells highlights its fundamental importance in eukaryotic translation.