Probable ATP-dependent RNA helicase. During immune response, may enhance IFNB1 expression via IRF3/IRF7 pathway (PubMed:30475900). ATP + H2O = ADP + H(+) + phosphate Shuttles between the nucleus and the cytoplasm in an XPO1-dependent manner. Found in heart, brain, liver, skeletal muscle, kidney and testis. Low expression detected in lung. In testis, expressed in all types of spermatogenic cells including spermatogonia, spermatocytes, spermatids and somatic Sertoli cells within the seminiferous tubules. Also expressed in Leydig cells and other interstitial cells. Knockout males show normal spermatogenesis, produce morphologically normal spermatozoa and sire healthy offspring (PubMed:30613052). DDX3X and DDX3Y double knockout is embryonic lethal (PubMed:30613052). DDX3X and DDX3Y double knockout germ cells can differentiate into spermatozoa (PubMed:30613052). Belongs to the DEAD box helicase family. DDX3/DED1 subfamily.