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Related Concept Videos

Ribosomal RNA Synthesis02:53

Ribosomal RNA Synthesis

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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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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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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Analysis of Translation Initiation During Stress Conditions by Polysome Profiling
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Dual function of eIF3j/Hcr1p in processing 20 S pre-rRNA and translation initiation.

L Valásek1, J Hasek, K H Nielsen

  • 1Laboratory of Gene Regulation and Development, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.

The Journal of Biological Chemistry
|September 19, 2001
PubMed
Summary

The protein eIF3j/Hcr1p is crucial for both translation initiation and the maturation of 40S ribosomal subunits, specifically by aiding in rRNA processing. This dual role links ribosome biogenesis directly to translation efficiency.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • eIF3j/Hcr1p is a known component of the eukaryotic translation initiation factor 3 (eIF3) complex.
  • Its role in stabilizing translation initiation complexes and binding to Met-tRNA(i)(Met) has been previously established.

Purpose of the Study:

  • To investigate the function of eIF3j/Hcr1p beyond its role in translation initiation.
  • To determine if eIF3j/Hcr1p plays a part in ribosome biogenesis.

Main Methods:

  • Immunofluorescence staining to determine cellular localization.
  • Analysis of mutant phenotypes (hcr1Δ) including subunit amounts, pre-rRNA levels, and growth defects.
  • Complementation studies using the human ortholog (heIF3j/p35).

Main Results:

  • eIF3j/Hcr1p is an RNA-binding protein predominantly localized in the cytoplasm.
  • hcr1Δ mutants show reduced 40S subunits, increased 20S pre-rRNA, and hypersensitivity to paromomycin.
  • The human ortholog heIF3j/p35 complements translation initiation but not the 40S biogenesis defect.

Conclusions:

  • eIF3j/Hcr1p is essential for efficient processing of 20S rRNA to 18S rRNA during 40S ribosome maturation.
  • This protein links ribosome biogenesis to translation initiation, highlighting a dual function.
  • The human ortholog can substitute for translation initiation but not ribosome biogenesis.