Identification of the enzyme that trims the 3'-end of piRNAs in silkworms

Piwi-interacting RNAs (piRNAs) are predominantly expressed in germline cells and function in transposon silencing. Unlike other small RNAs, piRNAs are processed from long single-stranded RNAs independently of Dicer. At the final step in piRNA biogenesis, 3' ends of precursor piRNAs (pre-piRNAs) that are longer than the mature length are trimmed by the exonuclease Trimmer in cooperation with its partner protein Papi, and subsequently 2'-O-methylated by Hen1, resulting in mature piRNAs. We performed piRNA profiling in silkworm BmN4 cells in which Trimmer and/or Papi have been depleted.