Myosins are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The term was originally used to describe a group of similar ATPases found in the cells of both striated muscle tissue and smooth muscle tissue. Following the discovery by Pollard and Korn (1973) of enzymes with myosin-like function in Acanthamoeba castellanii, a global range of divergent myosin genes have been discovered throughout the realm of eukaryotes.