The major myosin phosphatase in skeletal muscle is a complex between the beta-isoform of protein phosphatase 1 and the MYPT2 gene product.

Myosin is dephosphorylated by distinct forms of protein phosphatase 1 (PP1) in smooth muscle and skeletal muscle that are composed of PP1 complexed to different regulatory subunits. The smooth muscle myosin phosphatase (smPP1M) has been characterised previously and is composed of PP1beta complexed to M110 and M21 subunits that enhance the dephosphorylation of smooth muscle myosin, but not skeletal muscle myosin. In contrast, the regulatory subunit(s) of skeletal muscle myosin phosphatase (skPP1M) greatly enhance(s) the dephosphorylation of skeletal muscle myosin. Here we identify a regulatory subunit of skPP1M as the product of the MYPT2 gene, a protein whose sequence is 61% identical to the M110 subunit of smPP1M. Surprisingly, the M21 subunit of smPP1M appears to be produced from the same gene that encodes MYPT2.