Probable RNA helicase required for axial polarization of the oocyte during early and mid oogenesis. Plays a central role in RNA interference (RNAi) process, a process that mediates mRNA destruction of translational repression. Required for the assembly of the RISC complex, a complex required for target RNA destruction or repression. May be required in the RISC assembly to unwind miRNAs, in the production of single-stranded miRNA from the double-stranded miRNA, a key step in RISC formation. Required both for the translational control of oskar (osk) mRNA and cytoskeletal polarization in the oocyte. Required for somatic primary piRNA biogenesis. ATP + H2O = ADP + H(+) + phosphate Forms a complex with piwi and fs(1)Yb; this interaction is required for proper piRNA loading and nuclear localization of piwi. The interaction of piwi and fs(1)Yb is likely to occur via armi. Component of Yb bodies, an electron dense structure containing Yb protein found in somatic cells of ovary and testis. Abundant in oocytes and syncytial blastoderm. Expressed at low level throughout development, including somatic tissues. First apparent early in oogenesis, in the cytoplasm of stem cells and mitotically dividing cystoblasts. In regions 2a and 2b of the germarium, it is most concentrated in the center of the germline cysts, where the pro-oocyte is located. In stage 1 and early stage 2 egg chambers, it accumulates at the anterior of the oocyte, near the ring canals. It also extends through the ring canals forming a branched structure that links the early oocyte with adjacent nurse cells. In stage 3 cysts, it accumulates at the posterior cortex and localizes to extensions that pass through the oocyte into the nurse cells. Through stages 4 to 7, it continues to be somewhat enriched at the posterior cortex of the oocyte, but at significantly lower level. In stage 9 to 10 egg chambers, it is found throughout the cytoplasm of the oocyte and nurse cells, with slight enrichment at the oocyte cortex. Belongs to the DNA2/NAM7 helicase family. SDE3 subfamily.