Piwi and piRNA form the piRNA-induced silencing complex (piRISC) to repress transposons. In the current model, Armitage (Armi) brings the Piwi-piRISC precursor (pre-piRISC) to mitochondria, where Zucchini-dependent piRISC maturation occurs. Here, we show that Armi is necessary for Piwi-pre-piRISC formation at Yb bodies and that Armi triggers the exit of Piwi-pre-piRISC from Yb bodies and the translocation to mitochondria. Piwi-pre-piRISC resist leaving Yb bodies until Armi binds Piwi-pre-piRISC through the piRNA precursors. The lack of the Armi N-terminus also blocks the Piwi-pre-piRISC exit from Yb bodies. Thus, Armi determines Piwi-piRISC processing, in a multilayered manner, from precursor formation and quality control to inter-organelle translocation for maturation.

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