ATP-dependent RNA helicase involved nonsense-mediated mRNA decay and ribosome biogenesis through rRNA processing. ATP + H2O = ADP + H(+) + phosphate The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. May be due to competing acceptor splice site. Belongs to the DEAD box helicase family. DDX5/DBP2 subfamily.