Splicing of pre-mRNA requires the activity of at least eight different DEAD/H-box proteins that are involved in distinct steps of the splicing process. These proteins are driving the spliceosomal machinery by ATP-dependent unwinding of dsRNA and/or disrupting protein-RNA complexes. The spliceosomal DEAH-box proteins Prp2, Prp16, Prp22 and Prp43 share homologous C-terminal domains (CTD). We have determined the crystal structure of the CTD of human Prp22 by means of MAD. The fold of the human Prp22-CTD closely resembles that of the yeast Prp43-CTD. The similarity of these helicase-associated CTDs to the winged-helix and ratchet domains of the DNA helicase Hel308 suggests an analogous function in dsRNA binding and unwinding. Here, we also demonstrate that the CTD has a significant impact on the ATPase activity of yPrp22 in vitro. Homology modeling of the CTDs of hPrp2, hPrp16 and hPrp43 suggests that the CTDs of spliceosomal helicases contain conserved positively charged patches on their surfaces representing a common RNA-binding surface as well as divergent regions most likely mediating specific interactions with different proteins of the spliceosome.