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Related Concept Videos

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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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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.
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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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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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The flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma, which states that genes specify the sequence of mRNAs, which in turn specify the sequence of amino acids making up all proteins. The decoding of one molecule to another is performed by specific proteins and RNAs. Because the information stored in DNA is so central to cellular function, it makes intuitive sense that the cell would make mRNA copies of this information for protein synthesis...
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Related Experiment Video

Updated: Sep 25, 2025

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs
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Conformational rearrangements upon start codon recognition in human 48S translation initiation complex.

Sung-Hui Yi1, Valentyn Petrychenko2, Jan Erik Schliep2

  • 1Department of Physical Biochemistry, Max Planck Institute for Multidisciplinary Sciences, Göttingen 37077, Germany.

Nucleic Acids Research
|April 30, 2022
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Summary

Researchers studied human translation initiation, revealing two distinct ribosome states crucial for selecting the correct start codon. This provides new insights into protein synthesis regulation and differences between mammals and yeast.

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Biochemistry

Background:

  • Start codon selection is critical for accurate protein synthesis in human cells.
  • The 48S initiation complex plays a central role in this process.
  • Understanding the dynamic intermediates is key to deciphering translation regulation.

Purpose of the Study:

  • To elucidate the structural and kinetic mechanisms of human translation initiation.
  • To characterize the distinct ribosome conformations during start codon recognition.
  • To compare the start codon selection process in mammals versus yeast.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to determine structures of human 48S initiation complexes.
  • Kinetic assays using eukaryotic initiation factor 1A (eIF1A) as a reporter.
  • Analysis of ribosome populations in the presence of key initiation factors (eIF1, eIF1A, eIF2-GTP-Met-tRNAiMet, eIF3).

Main Results:

  • Two distinct ribosome populations ('open' and 'closed' conformations) were identified during initiation.
  • The 'open' state represents a pre-codon recognition intermediate, distinct from the scanning complex.
  • The 'closed' state resembles previously reported structures but features a unique eIF1A orientation; kinetic data reveal factor-mediated population shifts.
  • Differences in eIF1A orientation suggest mechanistic variations in start codon selection between mammals and yeast.

Conclusions:

  • The study provides structural and kinetic insights into human translation initiation intermediates.
  • Distinct conformations and factor dynamics are crucial for regulating start codon selection.
  • Identified differences highlight potential variations in translation initiation mechanisms between mammals and yeast.