PLD6 dimer cleaves primary piRNA transcript to pre-piRNA

As inferred from homologs in Drosophila and mouse, PLD6 (MitoPLD) located on the cytoplasmic face of the mitochondrial outer membrane makes the first endonucleolytic cleavage of primary piRNA transcripts. The cleavage yields a 5' phosphate and a 3' hydroxyl. Cleavage is believed to precede loading into PIWIL1 (HIWI, MIWI) or PIWIL2 (HILI, MILI). Most mature piRNAs have uracil at the 5' end. This appears to be due to selective binding by PIWI proteins rather than selective cleavage (reviewed in Bortvin 2013).

根据对果蝇和小鼠同源物的推断，位于线粒体外膜细胞质面的PLD6（MitoPLD）首先对原始piRNA转录本进行内切核酸酶切割。此切割过程产生了5'磷酸和3'羟基。据信，切割过程发生在加载至PIWIL1（HIWI，MIWI）或PIWIL2（HILI，MILI）之前。大多数成熟的piRNA在5'端含有尿嘧啶。这种现象似乎是由于PIWI蛋白的选择性结合而非选择性切割所致（参见Bortvin 2013年的综述）。