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Related Concept Videos

Initiation of Translation02:33

Initiation of Translation

38.0K
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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Initiation of Translation02:33

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Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70  chaperones are targetted to TOM20-TOM22 receptor complexes.
Most of the mitochondrial...
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Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death.  Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
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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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Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
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Related Experiment Video

Updated: Dec 18, 2025

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs
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Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs

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Distinct pre-initiation steps in human mitochondrial translation.

Anas Khawaja1,2, Yuzuru Itoh1,3, Cristina Remes4

  • 1Department of Medical Biochemistry and Biophysics, Division of Molecular Metabolism, Karolinska Institutet, Biomedicum, 171 65, Solna, Sweden.

Nature Communications
|June 12, 2020
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Summary

Human mitochondria use unique initiation factors (mtIF2, mtIF3) for protein synthesis. New research details two key assembly steps involving mS37, revealing how these factors form pre-initiation complexes.

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Rapid Isolation of the Mitoribosome from HEK Cells
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Related Experiment Videos

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Mitochondrial translation initiation in humans involves specialized factors (mtIF2, mtIF3) distinct from bacterial systems.
  • Understanding these unique factors is crucial for comprehending mitochondrial protein synthesis.

Purpose of the Study:

  • To elucidate the distinct steps in mitochondrial pre-initiation complex assembly.
  • To characterize the roles of mtIF2, mtIF3, and mS37 in initiating mitochondrial translation.

Main Methods:

  • Single-particle cryo-electron microscopy (cryo-EM) to visualize complex structures.
  • Fluorescence cross-correlation spectroscopy (FCCS) to analyze complex assembly dynamics.

Main Results:

  • Identified two distinct mitochondrial pre-initiation assembly steps.
  • Mitochondria-specific protein mS37 and mtIF3 stabilize the small mitoribosomal subunit for mtIF2 binding.
  • mtIF3 promotes assembly independently of mRNA and initiator tRNA, with its domains mediating exclusion.
  • Large mitoribosomal subunit association is essential for recruiting initiator tRNA and leaderless mRNA.

Conclusions:

  • Revealed novel mechanisms of mitochondrial translation initiation in mammals.
  • Detailed the sequential assembly pathway of the mitochondrial initiation complex.
  • Highlighted the unique roles of mtIF3 and mS37 in regulating mitoribosome function.