Fig. 2
From: Themes and variations on piRNA-guided transposon control
The combination of biogenesis and silencing modules differs for individual PIWI proteins in different organisms. A Primary (1°) piRNAs are generated by the endonuclease PLD6 (MitoPLD)/ Zucchini (ZUC) and its helicase partner MOV10L1/Armitage. A 5’ monophosporylated RNA fragment is loaded into a PIWI protein. The 3’ end of the mature piRNA is generated by another PLD6/ZUC cut, which is followed by exonucleolytic trimming in mice. Secondary (2°) piRNAs are generated by piRNA-guided slicing. The RNA helicase DDX4/Vasa partners with cytoplasmic PIWI slicers to load 5’ monophosphorylated cleavage fragments into another PIWI protein. During the effector phase, PIWI-piRNA complexes induce either transcriptional gene silencing (TGS) or post-transcriptional gene silencing (PTGS) depending on their subcellular localization and associated co-factors. B Individual PIWI proteins are either loaded with primary (dark green) or secondary (light green) piRNAs or both. Mature PIWI-piRNA complexes either induce TGS (purple) or PTGS (pink). (D.m. … Drosophila melanogaster; M.m. … Mus musculus; M. auratus … Mesocricetus auratus/ golden hamster)