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Related Experiment Videos

Initiation factor eIF5B catalyzes second GTP-dependent step in eukaryotic translation initiation.

Joon H Lee1, Tatyana V Pestova, Byung-Sik Shin

  • 1Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2716, USA.

Proceedings of the National Academy of Sciences of the United States of America
|December 10, 2002
PubMed
Summary

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Eukaryotic translation initiation requires GTP hydrolysis by both eIF2 and eIF5B. Unlike bacteria, human cells need eIF5B GTPase activity for protein synthesis and ribosomal subunit joining.

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Translation initiation factors IF2 (bacteria) and eIF2 (eukaryotes) are GTPases essential for binding Met-tRNA(i)(Met) to the small ribosomal subunit.
  • eIF5B is the eukaryotic homolog of bacterial IF2 and functions as a GTPase to facilitate ribosomal subunit joining during translation initiation.

Purpose of the Study:

  • To investigate the role of eIF5B GTPase activity in protein synthesis.
  • To determine the specific nucleotide requirements for eIF5B function in translation initiation.

Main Methods:

  • Site-directed mutagenesis of the conserved Asp-759 in human eIF5B to Asn.
  • Assays to measure GTPase activity and XTPase activity of wild-type and mutant eIF5B.
  • In vivo assays to assess the requirement of GTP or XTP for ribosomal subunit joining and translation initiation.

Related Experiment Videos

Main Results:

  • Mutation of Asp-759 in eIF5B converts its enzymatic activity from a GTPase to an XTPase.
  • The mutant eIF5B (Asp-759Asn) requires XTP, not GTP, for promoting ribosomal subunit joining and translation initiation.
  • GTPase activity of eIF5B is essential for its function in protein synthesis.

Conclusions:

  • Eukaryotic translation initiation necessitates GTP hydrolysis by both eIF2 and eIF5B.
  • This contrasts with bacterial translation initiation, where the single GTPase IF2 is sufficient.
  • The findings highlight distinct nucleotide requirements for translation initiation in prokaryotes and eukaryotes.