Involved in pre-mRNA splicing. Is required together with ATP and at least one other factor, for the first cleavage-ligation reaction. Functions as a molecular motor in the activation of the precatalytic spliceosome for the first transesterification reaction of pre-mRNA splicing by hydrolyzing ATP to cause the activation of the spliceosome without the occurrence of splicing. Capable of hydrolyzing nucleoside triphosphates in the presence of single-stranded RNAs such as poly(U). ATP + H2O = ADP + H(+) + phosphate Interacts directly with pre-mRNA. According to PubMed:2251118, associated with spliceosomes prior to and throughout step 1 of the splicing reaction. According to PubMed:8943336, it leaves the spliceosome before reaction 1. Interacts with SPP2. Present with 172 molecules/cell in log phase SD medium. Belongs to the DEAD box helicase family. DEAH subfamily.