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Related Concept Videos

pre-mRNA Processing02:01

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In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or pre-mRNA to distinguish it from mature mRNA.
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Splicing is the process by which eukaryotic RNA is edited before its translation into protein. The RNA strand transcribed from eukaryotic DNA is called the primary transcript. The primary transcripts that become mRNAs are called precursor messenger RNAs (pre-mRNAs). Eukaryotic pre-mRNA contains alternating sequences of exons and introns. Exons are nucleotide sequences that code for proteins, whereas introns are the non-coding regions. In RNA splicing, introns are removed and exons are bonded...
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One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the molecule. Altogether, these unusual bases protect the tRNA from enzymatic degradation by RNases.
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In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or pre-mRNA to distinguish it from mature mRNA.
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Alternative RNA splicing is the regulated splicing of exons and introns to produce different mature mRNAs from a single pre-mRNA. Unlike in constitutive splicing where a single gene produces a single type of mRNA, alternative splicing allows an organism to produce multiple proteins from a single gene and plays an important role in protein diversity.
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Updated: Sep 13, 2025

Extremely Rapid and Specific Metabolic Labelling of RNA In Vivo with 4-Thiouracil Ers4tU
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Queuosine is incorporated into precursor tRNA before splicing.

Wei Guo1,2,3, Igor Kaczmarczyk4,5, Kevin Kopietz6

  • 1Faculty of Biosciences, Heidelberg University, Heidelberg, Germany.

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|July 31, 2025
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Summary

Newly transcribed tRNA molecules require modifications for function. This study reveals that queuosine (Q) modification occurs before tRNA splicing in eukaryotes, clarifying a key step in tRNA maturation.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Transfer RNA (tRNA) molecules undergo extensive post-transcriptional modifications to become functional.
  • Queuosine (Q) is a crucial modification at position 34 of specific tRNAs, particularly those with GUN anticodons.
  • Eukaryotic tRNATyr precursors contain an intronic sequence in the anticodon loop that necessitates non-canonical splicing.

Purpose of the Study:

  • To investigate the temporal relationship between tRNA splicing and Q-modification in tRNATyr.
  • To determine if Q-incorporation precedes or follows the removal of the intronic sequence.
  • To elucidate the hierarchical coordination of these essential tRNA maturation steps.

Main Methods:

  • In vitro and in vivo biochemical assays.
  • Analysis of tRNATyr precursors in multiple model organisms (mouse, human, flies, worms).
  • Single particle cryo-electron microscopy (cryo-EM) of pre-tRNATyr with the QTRT1/2 complex.

Main Results:

  • Intron-containing tRNATyr precursors are modified with queuosine (Q) or galactosyl-queuosine (galQ) prior to splicing.
  • This sequence of Q-modification followed by splicing is conserved across diverse eukaryotic species.
  • Cryo-EM confirmed that pre-tRNATyr is a substrate for the QTRT1/2 complex, the enzyme responsible for Q incorporation.

Conclusions:

  • The study establishes a hierarchical order for tRNA maturation, with Q-modification preceding tRNA splicing for tRNATyr.
  • This finding clarifies a previously elusive aspect of cellular tRNA processing and functionalization.
  • The conserved mechanism highlights the importance of coordinated tRNA maturation pathways in eukaryotes.