Protein phosphatase that associates with over 200 regulatory proteins to form highly specific holoenzymes which dephosphorylate hundreds of biological targets. Protein phosphatase (PP1) is essential for cell division, it participates in the regulation of glycogen metabolism, muscle contractility and protein synthesis. Involved in regulation of ionic conductances and long-term synaptic plasticity. Component of the PTW/PP1 phosphatase complex, which plays a role in the control of chromatin structure and cell cycle progression during the transition from mitosis into interphase. In balance with CSNK1D and CSNK1E, determines the circadian period length, through the regulation of the speed and rhythmicity of PER1 and PER2 phosphorylation. May dephosphorylate CSNK1D and CSNK1E (By similarity). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate H2O + O-phospho-L-seryl-[myosin light chain] = L-seryl-[myosin light chain] + phosphate H2O + O-phospho-L-threonyl-[myosin light chain] = L-threonyl-[myosin light chain] + phosphate Binds 2 manganese ions per subunit. Inhibited by the toxins okadaic acid, tautomycin and microcystin Leu-Arg. The phosphatase activity of the PPP1R15A-PP1 complex toward EIF2S1 is specifically inhibited by Salubrinal, a drug that protects cells from endoplasmic reticulum stress (By similarity). PP1 comprises a catalytic subunit, PPP1CA, PPP1CB or PPP1CC, which is folded into its native form by inhibitor 2 and glycogen synthetase kinase 3, and then complexed to one or several targeting or regulatory subunits. The targeting or regulatory subunits determine the substrate specificity of PP1. PPP1R12A, PPP1R12B and PPP1R12C mediate binding to myosin. PPP1R3A (in skeletal muscle), PPP1R3B (in liver), PPP1R3C, PPP1R3D and PPP1R3F (in brain) mediate binding to glycogen. PPP1R15A and PPP1R15B mediate binding to EIF2S1. Part of a complex containing PPP1R15B, PP1 and NCK1/2. Interacts with PPP1R7 and PPP1R12C. Interacts with PPP1R16B. Component of the PTW/PP1 phosphatase complex, composed of PPP1R10/PNUTS, TOX4, WDR82, and PPP1CA or PPP1CB or PPP1CC. Interacts with PPP1R8. Interacts with PPP1R12A and NUAK1; the interaction is direct. Interacts with TRIM28; the interaction is weak. Interacts with FOXP3. Interacts with RRP1B. Interacts with SERPINE1. Interacts with LZTR1 (By similarity). Highly mobile in cells and can be relocalized through interaction with targeting subunits. In the presence of PPP1R8 relocalizes from the nucleus to nuclear speckles. Belongs to the PPP phosphatase family. PP-1 subfamily. The things we forget - Issue 32 of March 2003