For all we know about miRNA – how it’s made, what it does, how it folds, … – comparatively little is known about how the Argonaute (Ago) proteins allow miRNA to do what it does. Yet thanks to a group out of Germany, we now understand a bit more of the machinery that lets miRNA silence mRNA targets.
While Importin 8 (Imp8) doesn’t seem to bind directly to any RNAs itself, the newly-discovered P body protein does hook up with Ago proteins. The team paired up Ago2 pulldowns with microarrays and found that while Imp8 is required for Ago to efficiently bind a wide variety of its target mRNA, it helps target Ago to the nucleus, and depleting Imp8 interferes with miRNA-based gene silencing.
Whether Imp8 (with the help of other proteins) allows free Ago-miRNA complexes to find their target mRNA, alters the structure of Ago, or functions in some other capacity, is still yet to be determined. Place your bets after reading the full article at Cell , January 2009