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Vol. 309 no. 5740 pp. 1573-1576
DOI: 10.1126/science.1115079
  • Report

Inhibition of Translational Initiation by Let-7 MicroRNA in Human Cells

  1. Witold Filipowicz1,*
  1. 1 Friedrich Miescher Institute for Biomedical Research, 4002 Basel, Switzerland.
  2. 2 Institut de Génétique Moléculaire de Montpellier, 34000 Montpellier, France.
  1. * To whom correspondence should be addressed. E-mail: Filipowi{at}


MicroRNAs (miRNAs) are ∼21-nucleotide-long RNA molecules regulating gene expression in multicellular eukaryotes. In metazoa, miRNAs act by imperfectly base-pairing with the 3′ untranslated region of target messenger RNAs (mRNAs) and repressing protein accumulation by an unknown mechanism. We demonstrate that endogenous let-7 microribonucleoproteins (miRNPs) or the tethering of Argonaute (Ago) proteins to reporter mRNAs in human cells inhibit translation initiation. M7G-cap-independent translation is not subject to repression, suggesting that miRNPs interfere with recognition of the cap. Repressed mRNAs, Ago proteins, and miRNAs were all found to accumulate in processing bodies. We propose that localization of mRNAs to these structures is a consequence of translational repression.

  • Received for publication 20 May 2005.
  • Accepted for publication 22 July 2005.