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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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Translation in Prokaryotes01:29

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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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Translational Regulation01:29

Translational Regulation

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Translational regulation in prokaryotes ensures efficient protein synthesis by controlling ribosome access to mRNA. This regulation is mediated by secondary RNA structures, including translational riboswitches, RNA thermometers, and small RNAs (sRNAs), which respond to intracellular and environmental signals to modulate gene expression.Translational RiboswitchesRiboswitches in the leader region of mRNAs can regulate translation by altering the accessibility of the Shine-Dalgarno (SD) sequence,...
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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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Leaky Scanning02:28

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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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Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses
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Selective translation by alternative bacterial ribosomes.

Yu-Xiang Chen1,2, Zhi-Yu Xu1,3, Xueliang Ge4

  • 1Centre for Global Health and Infectious Diseases, Collaborative Innovation Centre for the Diagnosis and Treatment of Infectious Diseases, Tsinghua University School of Medicine, 100084 Beijing, China.

Proceedings of the National Academy of Sciences of the United States of America
|July 30, 2020
PubMed
Summary

Alternative bacterial ribosomes, distinct from canonical ones, show unique translational features and aid in adapting to harsh environments, particularly in iron homeostasis. This study provides direct evidence of their nonredundant roles.

Keywords:
alternative ribosomesmycobacteriumribosome profiling

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Area of Science:

  • Bacterial molecular biology
  • Ribosome biogenesis and function
  • Microbial adaptation and stress response

Background:

  • Alternative ribosome subunit proteins are common in bacteria, but their functions remain debated.
  • Previous studies relied on gene deletions, preventing direct comparison of ribosome isoforms within the same cell.
  • Understanding ribosomal heterogeneity is crucial for deciphering bacterial physiology and adaptation.

Purpose of the Study:

  • To directly compare the functional and translational characteristics of canonical and alternative ribosomes.
  • To investigate the role of alternative ribosomes in bacterial adaptation, specifically in response to iron availability.
  • To elucidate the distinct contribution of alternative ribosomes in *Mycobacterium smegmatis*.

Main Methods:

  • Simultaneous purification of canonical and alternative RpsR ribosomes from *Mycobacterium smegmatis*.
  • Ribosome profiling to assess differential gene translation efficiency.
  • Analysis of initiation complex formation in alternative ribosomes.
  • Phenotypic analysis of an *M. smegmatis* strain lacking the alternative ribosome protein operon under iron-depleted conditions.

Main Results:

  • Alternative ribosomes exhibit distinct translational features compared to canonical ribosomes.
  • Both ribosome types actively participate in protein synthesis, but with differential efficiency for specific gene sets.
  • Alternative ribosomes show a defect in initiation complex formation.
  • Deletion of the alternative ribosome protein operon impairs growth in iron-depleted medium, highlighting a role in iron homeostasis.

Conclusions:

  • Alternative bacterial ribosomes possess unique translational properties and are not redundant with canonical ribosomes.
  • These alternative ribosomes play a critical, nonredundant role in bacterial adaptation to challenging environments, such as iron scarcity.
  • The findings provide direct evidence for the functional significance of ribosomal heterogeneity in bacterial survival and homeostasis.