mRNP reorganization during microRNA-mediated repression

Although microRNAs are thought to impact nearly every mammalian biological process, their molecular mechanism remains controversial. Since all mRNAs are dressed with proteins to form mRNA-protein complexes (mRNPs), we reasoned that microRNAs might act by reorganizing target mRNPs. To test this hypothesis, we analyzed, on a transcriptome-wide scale, how the binding of core mRNP components (eIF4E, eIF4G and PABP) was affected by mammalian microRNA-mediated repression. Despite the transient nature of the repression intermediates, we found that microRNAs stimulated the reorganization of target mRNPs. Furthermore, although poly(A)-tail length has long been considered to be critical in post-transcriptional regulation, it was the binding of these core mRNP components, rather than poly(A)-tail length itself, that correlated with translational efficiency and mRNA stability. These results suggest that modulation of core mRNP components represents a key node in posttranscriptional gene regulation.