PT  - JOURNAL ARTICLE
AU  - Xiawei Huang
AU  - Hongmiao Hu
AU  - Alexandre Webster
AU  - Fan Zou
AU  - Jiamu Du
AU  - Katalin Fejes Toth
AU  - Alexei A. Aravin
AU  - Sisi Li
TI  - Binding of guide piRNA triggers methylation of the unstructured N-terminal region of Aub leading to assembly of the piRNA amplification complex
AID  - 10.1101/2020.07.14.203323
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.07.14.203323
4099  - http://biorxiv.org/content/early/2020/07/14/2020.07.14.203323.short
4100  - http://biorxiv.org/content/early/2020/07/14/2020.07.14.203323.full
AB  - Piwi proteins use guide piRNAs to repress selfish genomic elements, protecting the genomic integrity of gametes and ensuring the fertility of animal species. Efficient transposon repression depends on amplification of piRNA guides in the ping-pong cycle, which in Drosophila entails tight cooperation between two Piwi proteins, Aub and Ago3. Here we show that post-translational modification, symmetric dimethylarginine (sDMA), of Aub is essential for piRNA biogenesis, transposon silencing and fertility. Methylation is triggered by loading of a piRNA guide into Aub, which exposes its unstructured N-terminal region to the PRMT5 methylosome complex. Thus, sDMA modification is a signal that Aub is loaded with piRNA guide. Amplification of piRNA in the ping-pong cycle requires assembly of a tertiary complex scaffolded by Krimper, which simultaneously binds the N-terminal regions of Aub and Ago3. To promote generation of new piRNA, Krimp uses its two Tudor domains to bind Aub and Ago3 in opposite modification and piRNA-loading states. Our results reveal that post-translational modifications in unstructured regions of Piwi proteins and their binding by Tudor domains that are capable of discriminating between modification states is essential for piRNA biogenesis and silencing.HighlightssDMA modification of Aub is essential for ping-pong cycle, transposon silencing and fertility.piRNA loading triggers Aub sDMA modification by exposing its unstructured N terminal region to the methylosome complex.A single molecule of Krimp simultaneously binds piRNA-bound Aub and empty Ago3 to assemble ping-pong complex.The distinct structure of two Tudor domains of Krimp ensures binding of Ago3 and Aub in opposite modification and piRNA-loading states.Competing Interest StatementThe authors have declared no competing interest.