The cwf21 family is involved in mRNA splicing. It has been isolated as a subcomplex of the splicosome in Schizosaccharomyces pombe. The function of the cwf21 domain is to bind directly to the spliceosomal protein Prp8. Mutations in the cwf21 domain prevent Prp8 from binding. The structure of this domain has recently been solved which shows this domain to be composed of two alpha helices.