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 (By similarity). ATP + H2O = ADP + H(+) + phosphate Cells show pre-mRNA splicing defects. Cdc28-P8 temperature-sensitive mutant causes cell-cycle arrest in G2 and exhibits a splicing defect that leads to accumulation of unspliced precursors at the restrictive temperature. Temperature-sensitive pre-mRNA splicing mutant Prp8-1 exhibits a cell-cycle phenotype identical to cdc28-p8. Prp8-1 mutant produces elongated cells, accumulates U6 snRNA precursor and has defects in an early step of TFIID pre-mRNA splicing at the nonpermissive temperature. Belongs to the DEAD box helicase family. DEAH subfamily. DDX16/PRP8 sub-subfamily.