3′ End Formation of PIWI-Interacting RNAs In Vitro

▸ Establishment of a cell-free system recapitulating key steps of piRNA biogenesis ▸ PIWI proteins incorporate long pre-piRNAs with faithful 5′-nucleotide preference ▸ 3′ end of PIWI-loaded pre-piRNAs is trimmed by a Mg2+-dependent 3′ to 5′ exonuclease ▸ 2′-O-methylation of piRNA 3′ ends is tightly coupled with trimming