The effects of the 5' pocket motif of Dicer on miRNA biogenesis

A hallmark of RNA silencing is a class of ~22 nt RNAs which are processed from dsRNA precursor by Dicer. Accurate processing by Dicer is critical for the functionality of microRNAs (miRNAs). According to the current model, Dicer measures the length by anchoring the 3' overhang of the dsRNA terminus. Here we find that human Dicer binds to the 5' end of RNA and utilizes the 5' end as an additional reference point for cleavage site selection (5' counting rule). We further identify a novel motif (5'-pocket) in Dicer, which recognizes the 5' end of RNA. By analyzing miRNA population from 5'-pocket mutant Dicer expressing Dicer-null mES, we provide that the 5' pocket is significant for Dicer processing in vivo. Examination of small RNA profiles from Dicer-null mouse embryonic stem cells transfected with either wild-type or 5' pocket mutant Dice expression plasmids.