piRNA biogenesis requires which enzyme?
Unlike siRNA and miRNA requiring Dicer RNase III and Drosha, piRNA biogenesis proceeds independently of those enzymes. Primary piRNAs derive from long single-stranded precursors transcribed from piRNA clusters, cleaved by mitochondrial endonuclease Zucchini PLD6 trimming 5' ends, followed by 3' trimming via exonuclease Nibbler and 2'-O-methylation by Hen1 stabilizing terminus. Amplification via ping-pong between PIWI proteins Aubergine and Ago3 slicing targets generates secondary piRNAs without Dicer. Hence standard RNAi enzymes dispensable, explaining answer none. This alternative biogenesis
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: piRNA Biogenesis Independent of Dicer and Drosha
