Cdc40, also known as pre-mRNA-processing factor 17 (PRPF17) or EH-binding protein 3 (EHB3), is a 579 amino acid nuclear protein. Cdc40 is essential for the catalytic step II of the pre-mRNA splicing process, in which Cdc40 associates with the spliceosome C complex. Cdc40 contains seven WD repeats, which are important in protein-protein interactions. Cdc40 has sequence similarity to the yeast protein Prp17, which is involved in pre-mRNA splicing and cell cycle progression. The sequence similarity between the mammalian Cdc40 and the yeast Prp17 may indicate an additional role in cell cycle progression for mammalian Cdc40.