Regulates myosin phosphatase activity. PP1 comprises a catalytic subunit, PPP1CA, PPP1CB or PPP1CC, and one or several targeting or regulatory subunits (By similarity). PPP1R12A mediates binding to myosin. Also along actomyosin filaments. Detected in brain, lung, aorta, heart, gizzard, stomach, oviduct, spleen, kidney and small intestine. Phosphorylated by CIT (Rho-associated kinase) and by ROCK2 on serine and threonine residues. Phosphorylation at Thr-695 leads to inhibition of myosin phosphatase activity. Phosphorylation at Thr-850 abolishes myosin binding. May be phosphorylated at Thr-695 by DMPK; may inhibit the myosin phosphatase activity.