This domain family is found in eukaryotes, and is approximately 100 amino acids in length. The family is found in association with pfam10197. There is a single completely conserved residue Y that may be functionally important. Cwc25 has been identified to associate with pre-mRNA splicing factor Cef1/Ntc85, a component of the Prp19-associated complex (NTC) involved in spliceosome activation. Cwc25 is neither tightly associated with NTC nor required for spliceosome activation, but is required for the first catalytic reaction.