ATP-binding RNA helicase involved in transcription elongation and required for the export of mRNA out of the nucleus. SUB2 also plays a role in pre-mRNA splicing and spliceosome assembly. May be involved in rDNA and telomeric silencing, and maintenance of genome integrity. Links the mRNA adapter mlo3 to rae1 for targeting mRNA-protein complex to the proteins of the nucleoporin complex (NPC). ATP + H2O = ADP + H(+) + phosphate Interacts with mlo3 and rae1. 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. DECD subfamily.