Nature 426, 469–474 (2003).

In this Letter, the last two sentences of the second paragraph of the left column on page 470 should read: “Preliminary data using an immobilized 5′ phosphorylated ssRNA with a 3′-biotin modification showed that this RNA failed to pull down purified Ago1 PAZ domain (data not shown). By NMR titration, this RNA had a reduced binding affinity (Kd greater than 20 µM), suggesting that the 3′ end may also play a role in PAZ domain interaction.”