The consequences of protein regulation by microRNAs (miRNAs) are studied on a large scale in two papers published online in Nature. The results show that changing the levels of just one miRNA can, in some cases, affect the expression levels of hundreds of proteins. The studies also show that it may be possible to predict which genes miRNAs will interact with, although the science is far from exact at present.
miRNAs act on a gene's messenger RNA (mRNA) to affect how much protein is made by that gene. miRNAs can downregulate protein expression in two ways: by causing degradation of the mRNA or by inhibiting translation of the mRNA. Previous work examined how mRNA levels were affected by miRNA expression, but because no large study of how protein levels were affected had been performed, the contribution of translational repression could not be estimated. In these studies two teams, Matthias Selbach and Nikolaus Rajewsky and colleagues and David Bartel and his team, use mass spectrometry to measure how many proteins in a cell show a change in their levels when a particular miRNA is present. This is the first time researchers have measured tangibly the effect of miRNAs on cellular protein levels, and the work shows that, although the amount of expression change is modest in most cases, the scale of the effects is widespread.
Matthias Selbach (Max Delbrueck Center for Molecular Medicine, Berlin, Germany) Author paper 
Nikolaus Rajewsky (Max Delbruck Center for Molecular Medicine, Berlin, Germany) Co-author paper 
David Bartel (Whitehead Institute, Massachusetts Institute of Technology, Cambridge, MA, USA) Author paper 
Abstracts available online:
(C) Nature press release.
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