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Initiation of Translation02:33

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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.
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eIF5 and eIF5B together stimulate 48S initiation complex formation during ribosomal scanning.

Vera P Pisareva1, Andrey V Pisarev1

  • 1Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Ave, Brooklyn, NY 11203, USA andrey.pisarev@downstate.edu.

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Summary

Eukaryotic translation initiation factors eIF5 and eIF5B together enhance 48S initiation complex (48S IC) formation. They specifically improve selection of non-optimal start codons during ribosomal scanning by influencing GTP hydrolysis and complex stability.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • 48S initiation complex (48S IC) formation is the crucial first step in eukaryotic translation.
  • The canonical model describes 40S ribosomal subunit binding to mRNA and scanning to the initiation codon, mediated by initiation factors.

Purpose of the Study:

  • To investigate the roles of eIF5 and eIF5B in 48S IC formation and initiation codon selection.
  • To elucidate the mechanism by which eIF5 and eIF5B influence ribosomal scanning and start codon recognition.

Main Methods:

  • Mutational analysis of initiation factors eIF1A and eIF5B.
  • Biochemical assays to study 48S IC formation and GTP hydrolysis.
  • Investigating the impact of mRNA structure and start codon context on initiation.

Main Results:

  • eIF5 and eIF5B together stimulate 48S IC formation, particularly at non-optimal start codons.
  • eIF5-induced GTP hydrolysis of eIF2 is essential for this stimulation, increasing recognition of non-optimal codons.
  • eIF5B stabilizes the initiator tRNA in the P site of the 40S subunit for less stable 48S ICs.
  • Mutational analysis revealed distinct functions for eIF5B in 48S IC formation and subunit joining.

Conclusions:

  • eIF5 and eIF5B play a coordinated role in promoting 48S IC formation and refining initiation codon selection during ribosomal scanning.
  • The findings support a model where eIF5 promotes GTP hydrolysis for better start codon recognition, and eIF5B stabilizes the resulting complex.
  • Distinct roles of eIF5B in both 48S IC formation and later stages of translation initiation were identified.