Involved in the piwi-interacting RNA (piRNA) metabolic process, which mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins, and governs the methylation and subsequent repression of transposons which is essential for germline integrity (PubMed:21447556, PubMed:29531043). Likely to act by recruiting Piwi proteins such as AGO3 and piwi to the piRNA biogenesis machinery in the nuage (PubMed:21447556, PubMed:29531043). Required for the final steps of primary piRNA biogenesis by participating in the 3' end-trimming of piwi-bound intermediates into mature piRNAs (PubMed:29531043). Interacts (via C-terminus) with AGO3 (via the N-terminal region when symmetrically methylated on arginine residues); this interaction is RNA-independent and may be required for AGO3 localization to the nuage (PubMed:21447556). Interacts (via Tudor domain) with piwi (via N-terminus) (PubMed:21447556, PubMed:29531043). Interacts with tral and me31B (PubMed:21447556). Component of the meiotic nuage, also named P granule, a germ-cell-specific organelle required to repress transposon activity during meiosis. Expressed in the cytoplasm of germline stem cells, cyst cells, nurse cells and oocytes, with strong accumulation in region IIb germline cysts in the germarium. In post-germarium egg chambers accumulates in the perinuclear loci that appear to be the nuage. Ovaries (at protein level). Expressed in the ovary and testis. Embryo (at protein level) (PubMed:21447556). Expressed throughout development with highest levels of expression in 3rd-instar larvae and adults (PubMed:21447556). Expressed throughout the whole early embryo including the pole cells (PubMed:21447556). The Tudor domain is sufficient for binding to the N-terminus (1-14) of both unmethylated piwi or piwi symmetrically dimethylated at 'Arg-10' (PubMed:29531043). However, it may not be sufficient for binding to symmetrically dimethylated AGO3, instead this interaction may require a larger region of the C-terminus which includes the Tudor domain (257-576) (PubMed:21447556, PubMed:29531043). RNAi-mediated knockdown does not produce a visible phenotype. However, fertility is reduced with egg-laying decreased by 30%. AGO3 protein levels are decreased and AGO3 is delocalized from the nuage. No effect on nuage morphology and no mislocalization of piwi and aub. RNAi-mediated knockdown in germline tissues results in delocalization of AGO3 from the nuage. Belongs to the Tdrkh family.