Siwi cooperates with Par-1 kinase to resolve the autoinhibitory effect of Papi for Siwi-piRISC biogenesis

• Published in: Nature communications Vol. 13; no. 1; p. 1518
• Main Authors: Yamada, Hiromi, Nishida, Kazumichi M, Iwasaki, Yuka W, Isota, Yosuke, Negishi, Lumi, Siomi, Mikiko C
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 21.03.2022; Nature Publishing Group UK; Nature Portfolio
• Subjects: Animals; Biosynthesis; Bombyx - metabolism; DNA damage; Domains; Genomes; Germ cells; Homology; Kinases; Mitochondria; Mutants; Phosphorylation; Precursors; Proteinase-activated receptor 1; RNA, Small Interfering - genetics; RNA, Small Interfering - metabolism; Transposons; Tudor Domain
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-29193-9

Bombyx Papi acts as a scaffold for Siwi-piRISC biogenesis on the mitochondrial surface. Papi binds first to Siwi via the Tudor domain and subsequently to piRNA precursors loaded onto Siwi via the K-homology (KH) domains. This second action depends on phosphorylation of Papi. However, the underlying mechanism remains unknown. Here, we show that Siwi targets Par-1 kinase to Papi to phosphorylate Ser547 in the auxiliary domain. This modification enhances the ability of Papi to bind Siwi-bound piRNA precursors via the KH domains. The Papi S547A mutant bound to Siwi, but evaded phosphorylation by Par-1, abrogating Siwi-piRISC biogenesis. A Papi mutant that lacked the Tudor and auxiliary domains escaped coordinated regulation by Siwi and Par-1 and bound RNAs autonomously. Another Papi mutant that lacked the auxiliary domain bound Siwi but did not bind piRNA precursors. A sophisticated mechanism by which Siwi cooperates with Par-1 kinase to promote Siwi-piRISC biogenesis was uncovered.