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 PPI co mplexed to different regulatory subunits, The smooth muscle myosin pho sphatase (smPP1M) has been characterised previously and is composed of PP1 beta complexed to M-110 and M-21 subunits that enhance the dephos phorylation of smooth muscle myosin, but not skeletal muscle myosin. I n contrast, the regulatory subunit(s) of skeletal muscle myosin phosph atase (skPP1M) greatly enhance(s) the dephosphorylation of skeletal mu scle myosin. Here me identify a regulatory subunit of skPP1M as the pr oduct of the MYPT2 gene, a protein whose sequence is 61% identical to the M-110 subunit of smPP1M, Surprisingly, the M-21 subunit of smPP1M appears to be produced from the same gene that encodes MYPT2. (C) 1998 Federation of European Biochemical Societies.