Probable ATP-dependent RNA helicase. Component of the nucleolar ribosomal RNA (rRNA) processing machinery that regulates 3' end formation of ribosomal 47S rRNA. ATP + H2O = ADP + H(+) + phosphate Associates with PeBoW complex, composed of BOP1, PES1 and WDR12. Interacts directly with BOP1 and PES1. Associates with 60S and 90S pre-ribosomal particles. The C-terminal domain regulates nucleolar localization. Belongs to the DEAD box helicase family. DDX27/DRS1 subfamily.