ATP-dependent RNA helicase associated with the nuclear pore complex and essential for mRNA export from the nucleus. May participate in a terminal step of mRNA export through the removal of proteins that accompany mRNA through the nucleopore complex. May also be involved in early transcription (By similarity). ATP + H2O = ADP + H(+) + phosphate Associates with the nuclear pore complex. Nuclear pore complex cytoplasmic fibrils. The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. Belongs to the DEAD box helicase family. DDX19/DBP5 subfamily.