1. Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, Massachusetts 02142, USA
2. Howard Hughes Medical Institute and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Department of Cell Biology, 240 Longwood Avenue, Harvard Medical School, Boston, Massachusetts 02115, USA
4. These authors contributed equally to this work.

Correspondence to: Steven P. Gygi³David P. Bartel^1,2 Correspondence and requests for materials should be addressed to S.P.G. (Email: steven_gygi@hms.harvard.edu) or D.P.B (Email: dbartel@wi.mit.edu).

Abstract

MicroRNAs are endogenous 23-nucleotide RNAs that can pair to sites in the messenger RNAs of protein-coding genes to downregulate the expression from these messages. MicroRNAs are known to influence the evolution and stability of many mRNAs, but their global impact on protein output had not been examined. Here we use quantitative mass spectrometry to measure the response of thousands of proteins after introducing microRNAs into cultured cells and after deleting mir-223 in mouse neutrophils. The identities of the responsive proteins indicate that targeting is primarily through seed-matched sites located within favourable predicted contexts in 3' untranslated regions. Hundreds of genes were directly repressed, albeit each to a modest degree, by individual microRNAs. Although some targets were repressed without detectable changes in mRNA levels, those translationally repressed by more than a third also displayed detectable mRNA destabilization, and, for the more highly repressed targets, mRNA destabilization usually comprised the major component of repression. The impact of microRNAs on the proteome indicated that for most interactions microRNAs act as rheostats to make fine-scale adjustments to protein output.

1. Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, Massachusetts 02142, USA
2. Howard Hughes Medical Institute and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Department of Cell Biology, 240 Longwood Avenue, Harvard Medical School, Boston, Massachusetts 02115, USA
4. These authors contributed equally to this work.

Correspondence to: Steven P. Gygi³David P. Bartel^1,2 Correspondence and requests for materials should be addressed to S.P.G. (Email: steven_gygi@hms.harvard.edu) or D.P.B (Email: dbartel@wi.mit.edu).

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