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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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Initiation of Translation02:33

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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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Termination of Translation01:44

Termination of Translation

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The large ribosomal subunit has several important structures essential to translation. These include the peptidyl transferase center (PTC) - which is the site where the peptide bond is formed - and a large, internal, water-filled tube through which the nascent polypeptide moves. This latter structure is called the Peptide Exit Tunnel, and it begins at the PTC and spans the body of the large ribosomal subunit. During translation, as the nascent polypeptide chain is synthesized, it passes through...
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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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Xenopus laevis as a Model to Identify Translation Impairment
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Translation initiation factor eIF3 promotes programmed stop codon readthrough.

Petra Beznosková1, Susan Wagner2, Myrte Esmeralda Jansen2

  • 1Laboratory of Regulation of Gene Expression, Institute of Microbiology ASCR, Videnska 1083, Prague 142 20, the Czech Republic Faculty of Science, Charles University, Vinicna 5, Prague 128 44, the Czech Republic.

Nucleic Acids Research
|May 1, 2015
PubMed
Summary

Translation initiation factor eIF3 promotes programmed stop codon readthrough by interfering with release factor 1. This mechanism enhances proteome diversity by enabling C-terminally extended proteins and is conserved in yeast and humans.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Programmed stop codon readthrough increases proteome diversity by producing C-terminally extended proteins.
  • This process involves near-cognate tRNAs decoding stop codons, but the mechanism is poorly understood.
  • Competition between release factors and tRNAs at stop codons is context-dependent.

Purpose of the Study:

  • To elucidate the molecular mechanism of programmed stop codon readthrough.
  • To identify factors that promote readthrough on all three stop codons.
  • To investigate the role of translation initiation factor eIF3 in this process.

Main Methods:

  • Biochemical assays to study translation termination and readthrough.
  • Analysis of pre-termination complexes and factor interactions.
  • Comparative studies in yeast and human systems.

Main Results:

  • Translation initiation factor eIF3, not termination factors, promotes programmed readthrough.
  • eIF3 associates with pre-termination complexes and interferes with eRF1 decoding at the stop codon.
  • This interference allows near-cognate tRNAs with wobble position mismatches to incorporate amino acids.

Conclusions:

  • eIF3 is a key regulator of programmed stop codon readthrough.
  • The mechanism involves eIF3 modulating stop codon recognition by eRF1.
  • This conserved mechanism expands proteome diversity through C-terminal protein extension.