All known myosin phosphatases consist of PP1 beta and both a large and a small myosin phosphatase targetting (Mypt) subunit. The large Mypt targets PP1 beta to myosin and determines the substrate specifity of the phosphatase. The Large Mypt subunit is encoded by one of three human genes, PPP1R12A (MYPT1), PPP1R12B (MYPT2) and PPP1R12C. Only MYPT1 is represented here. The small subunit is an alternative transcript of MYPT2. The function of the small Mypt subunit remains unclear, but because it is known to interact directly with myosin and the large Mypt it is thought to have an unspecified regulatory role.