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. Interacts with NUP159, GLE1, GFD1 and ZDS1. The interaction with NUP159 is necessary for the association to the nuclear pore complex. Interacts also with the TFIIH complex subunits TFB1, TFB2 and RAD3 (By similarity). 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.