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Related Concept Videos

Transcription Elongation Factors02:35

Transcription Elongation Factors

Transcription elongation is a dynamic process that alters depending upon the sequence heterogeneity of the DNA being transcribed. Hence, it is not surprising that the elongation complex's composition also varies along the way while transcribing a gene.
The transcription elongation is regulated via pausing of RNA polymerase on several occasions during transcription. In bacteria, these halts are necessary because the transcription of DNA into mRNA is coupled to the translation of that mRNA into a...
Transcription Elongation Factors02:35

Transcription Elongation Factors

Transcription elongation is a dynamic process that alters depending upon the sequence heterogeneity of the DNA being transcribed. Hence, it is not surprising that the elongation complex's composition also varies along the way while transcribing a gene.
The transcription elongation is regulated via pausing of RNA polymerase on several occasions during transcription. In bacteria, these halts are necessary because the transcription of DNA into mRNA is coupled to the translation of that mRNA into a...
Transcription Initiation01:47

Transcription Initiation

Initiation is the first step of transcription in eukaryotes. Prokaryotic RNA Polymerase (RNAP) can bind to the template DNA and start transcribing. On the other hand, transcription in eukaryotes requires additional proteins, called transcription factors, to first bind to the promoter region in the DNA template. This binding helps recruit the specific RNAP that can assemble on the DNA and start transcription.
The promoters and enhancers and their accessory proteins allow tight regulation of...
Initiation of Translation02:33

Initiation of Translation

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...
Initiation of Translation02:33

Initiation of Translation

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...
Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...

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Updated: May 9, 2026

Artificial RNA Polymerase II Elongation Complexes for Dissecting Co-transcriptional RNA Processing Events
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Artificial RNA Polymerase II Elongation Complexes for Dissecting Co-transcriptional RNA Processing Events

Published on: May 13, 2019

Initiation with elongator tRNAs.

Laasya Samhita1, Kai Virumäe, Jaanus Remme

  • 1Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India.

Journal of Bacteriology
|July 16, 2013
PubMed
Summary

Cells can use elongator transfer RNAs (tRNAs) to initiate protein synthesis by altering initiator tRNA levels or increasing elongator tRNA abundance. This finding blurs the evolutionary distinction between initiator and elongator tRNAs.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Initiator tRNA (tRNAi) exclusively starts protein synthesis, while elongator tRNAs (tRNAe) extend polypeptide chains.
  • tRNAi possesses unique features for P-site binding and preferential translation initiation.
  • Recent findings highlight the role of tRNAi abundance in its specialized function.

Purpose of the Study:

  • To investigate if elongator tRNAs can initiate protein synthesis under specific cellular conditions.
  • To explore the impact of altered tRNA levels on translation initiation.
  • To understand the potential for generating proteome diversity via non-canonical initiation.

Main Methods:

  • Introduction of non-AUG initiation codons (CCC, GAG, GGU, UCU, UGU, ACG, AAU, AGA) into a reporter gene (ung).

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Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs
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  • Assays of enzyme activity in cells with reduced initiator tRNA levels and in stationary phase.
  • Overexpression of cognate elongator tRNAs using plasmid-borne genes.

    • Main Results:

    • Initiation from non-AUG codons was observed when intracellular initiator tRNA levels were reduced.
    • Non-AUG initiation activity significantly increased in stationary phase cells.
    • Further increases in non-AUG initiation occurred upon introduction of plasmid-borne elongator tRNAs.

    Conclusions:

    • Elongator tRNAs can initiate translation from non-AUG codons under conditions of reduced initiator tRNA abundance or increased elongator tRNA levels.
    • This mechanism may generate proteome diversity under stress without compromising genomic integrity.
    • Altering the relative amounts of initiator and elongator tRNAs blurs their traditionally distinct roles in protein synthesis.