Myosin phosphatase target subunit 1 (MBS), also known as the myosin-binding subunit of myosin phosphatase, is a key subunit of myosin phosphatase. It regulates actin-myosin interactions downstream of the Rho GTPase. Rho is involved in myosin light chain (MLC) phosphorylation, which triggers smooth muscle contraction and actin-myosin interaction in nonmuscle cells. The active form of RhoA (GTP.RhoA) specifically interacts with MBS, regulating MLC phosphorylation. Rho-kinase, activated by GTP.RhoA, phosphorylates MBS and inactivates myosin phosphatase. Overexpression of RhoA in NIH 3T3 cells increases MBS and MLC phosphorylation. Thus, Rho inhibits myosin phosphatase via Rho-kinase. Several transcript variants encoding different isoforms have been identified for this gene.