ATP-dependent RNA helicase involved in 40S ribosomal subunit biogenesis. Required for the processing and cleavage of 35S pre-rRNA at sites A0, A1, and A2, leading to mature 18S rRNA. ATP + H2O = ADP + H(+) + phosphate Associates in the nucleolus with the 60S and pre-60S ribosomal subunits. 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. DDX18/HAS1 subfamily.