MRCK stands for Myotonic dystrophy-Related Cdc42-binding Kinase. The protein earned this name because it binds to Cdc42 with a significant homology to the DMPK (Dystrophia Myotonica Protein Kinase) kinase domain. Prior to the identification of MRCK, many of the RHO-family GTPase effectors homologous to MRCK were discovered. After the identification of the RHO-family GTPases, Rho, Rac1, and Cdc42 (Manser et al. 1994), each of which plays distinctive roles in cytoskeletal reorganization associated with growth and differentiation, the search began for the interacting proteins and potential targets of the p21 (Cdc42/Rac) Rho family that might convey signals downstream...