Cell cycle events are regulated by the sequential activation and deactivation of cyclin dependent kinases (Cdks) and by the proteolysis of cyclins. The cell division control (Cdc) genes are required at various points in the cell cycle. 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.