Cell division control protein 42 homolog (Cdc42 or CDC42) is a protein that in humans is encoded by the CDC42 gene. Cdc42 is involved in regulation of the cell cycle. It was originally identified in S. cerevisiae (yeast) as a mediator of cell division,[5][6] and is now known to influence a variety of signaling events and cellular processes in a variety of organisms from yeast to mammals.