Of seeds and supplements: structural insights into extended microRNA-target pairing.

Metazoan micro(mi) RNAs guide Argonaute proteins to their targets via perfect pairing to the seed region, located near the 5' end of the miRNA. In this issue of The EMBO Journal, Sheu-Gruttadauria et al report the crystal structure of human Argonaute 2 in complex with both a miRNA and target RNA and show that miRNA 3' supplementary nucleotides can increase target affinity and may contribute more to miRNA-mediated silencing than is currently appreciated.