MicroRNA-mediated mRNA deadenylation and repression of protein synthesis in a mammalian cell-free system.

Cell-free systems are valuable tools for analyses of a post-transcriptional gene expression. The biochemical aspects of RNA interference have been extensively studied by using extracts prepared from Drosophila embryos. However, the mechanism by which microRNAs regulate protein synthesis is still elusive. We established a mammalian cell-free system that recapitulates let-7 microRNA-mediated repression of protein synthesis. Using this system, we found that a target mRNA was deadenylated when it was translationally repressed. The experimental data strongly suggested that the deadenylation was a cause, but not a result, of translational repression. In this chapter, we describe our cell-free system and discuss the significance of microRNA-mediated mRNA deadenylation in the repression of protein synthesis.