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Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs
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MicroRNAs control translation initiation by inhibiting eukaryotic initiation factor 4E/cap and poly(A) tail function

David T Humphreys1, Belinda J Westman, David I K Martin

  • 1Molecular Genetics Program, Victor Chang Cardiac Research Institute (VCCRI), 384 Victoria Street, Darlinghurst (Sydney) NSW 2010, Australia.

Proceedings of the National Academy of Sciences of the United States of America
|November 17, 2005
PubMed

Insights

MicroRNAs (miRNAs) repress mRNA translation by targeting the 5' cap and 3' poly(A) tail. These findings reveal that miRNAs interfere with translation initiation, implicating eukaryotic initiation factor 4E.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • MicroRNAs (miRNAs) are key regulators of gene expression.
  • miRNAs primarily function by inhibiting mRNA translation.
  • The precise mechanism of miRNA-mediated translational repression remains incompletely understood.

Purpose of the Study:

  • To elucidate the mechanism of miRNA-mediated translational repression.
  • To investigate the roles of the 5' cap and 3' poly(A) tail in miRNA function.
  • To identify molecular targets of miRNA action during translation.

Main Methods:

  • In vitro transcription of engineered mRNAs with multiple miRNA-binding sites.
  • Transfection of HeLa cells with mRNAs and cognate miRNAs.
  • Analysis of mRNA translation efficiency under different initiation conditions.

Main Results:

  • Both the 5' cap and 3' poly(A) tail are essential, but not sufficient, for full miRNA repression.
  • Replacing the 5' cap with an internal ribosome entry site (IRES) significantly reduced miRNA repression.
  • miRNA-mediated repression was impaired when cap-dependent translation initiation was bypassed.

Conclusions:

  • MicroRNAs interfere with the initiation step of mRNA translation.
  • The 5' cap structure is crucial for efficient miRNA-mediated translational repression.
  • Eukaryotic initiation factor 4E (eIF4E) is implicated as a direct or indirect molecular target of miRNA action.

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