N-terminal 6His-tagged recombinant, human MST4 amino acids 4-304.MST4 is a member of the GCK group III family of kinases, which are a subset of the Ste20-like kinases. This protein kinase contains an amino-terminal kinase domain, and a carboxy-terminal regulatory domain that mediates homodimerization. The protein kinase localizes to the Golgi apparatus and is specifically activated by binding to the Golgi matrix protein GM130. It is also cleaved by caspase-3 in vitro, and may function in the apoptotic pathway.