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 Optimum pH is 6.5. Active from pH 5 to 8. Interacts with RRP1. Associates in the nucleolus with the 60S and pre-60S ribosomal subunits. It has also been isolated with the nuclear pore complex. The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. Phosphorylated by CDK1. Transcription depends partially on SET1. Belongs to the DEAD box helicase family. DDX18/HAS1 subfamily.