ATP-dependent RNA helicase involved in mRNA turnover, and more specifically in mRNA decapping by activating the decapping enzyme DCP1. Is involved in G1/S DNA-damage checkpoint recovery, probably through the regulation of the translational status of a subset of mRNAs. May also have a role in translation and mRNA nuclear export (By similarity). ATP + H2O = ADP + H(+) + phosphate Is concentrated in several cytoplasmic foci called P bodies (or cytoplasmic processing bodies) which represent sites of mRNA decapping and 5' to 3' exonucleotidic decay. 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. DDX6/DHH1 subfamily.