Key regulator of protein phosphatase 1C (PPP1C). Mediates binding to myosin. As part of the PPP1C complex, involved in dephosphorylation of PLK1. Capable of inhibiting HIF1AN-dependent suppression of HIF1A activity (By similarity). PP1 comprises a catalytic subunit, PPP1CA, PPP1CB or PPP1CC, and one or several targeting or regulatory subunits. PPP1R12A mediates binding to myosin. Interacts with ARHA and CIT (By similarity). Binds PPP1R12B, ROCK1 and IL16. Interacts directly with PRKG1. Non-covalent dimer of 2 dimers; PRKG1-PRKG1 and PPP1R12A-PPP1R12A. Interacts with SMTNL1 (By similarity). Interacts with PPP1CB; the interaction is direct. Interacts (when phosphorylated at Ser-445, Ser-472 and Ser-910) with 14-3-3. Interacts with ROCK1 and ROCK2. Interacts with isoform 1 and isoform 2 of ZIPK/DAPK3. Interacts with RAF1. Interacts with HIF1AN (By similarity). Interacts with NCKAP1L (By similarity). Also along actomyosin filaments. Expressed in striated and vascular smooth muscle, specificcally in type 2a fibers (at protein level). Expression levels are 20-30% higher in developed males than females (at protein level). In neonates, expressed at low levels in striated and smooth muscles. As the animals mature sexually, expression increases 10-20-fold. Pregnancy promotes a 2-3-fold increase in expression in striated, vascular and uterine muscle (at protein level). Expressed in the prosencephalic neural folds at 8.5 dpc. Expressed in the lower urinary tract, specifically in epitheliumof the bladder, urethra, and genital tubercle at 13.5 dpc (PubMed:31883643). Heterotetramerization is mediated by the interaction between a coiled-coil of PRKG1 and the leucine/isoleucine zipper of PPP1R12A/MBS, the myosin-binding subunit of the myosin phosphatase. The KVKF motif mediates interaction with PPP1CB. Phosphorylated by CIT (Rho-associated kinase) (By similarity). Phosphorylated cooperatively by ROCK1 and CDC42BP on Thr-694 (By similarity). Phosphorylated on upon DNA damage, probably by ATM or ATR. In vitro, phosphorylation of Ser-693 by PKA and PKG appears to prevent phosphorylation of the inhibitory site Thr-694, probably mediated by PRKG1. Phosphorylation at Ser-445, Ser-472 and Ser-909 by NUAK1 promotes interaction with 14-3-3, leading to inhibit interaction with myosin light chain MLC2, preventing dephosphorylation of MLC2. May be phosphorylated at Thr-694 by DMPK; may inhibit the myosin phosphatase activity (By similarity). Phosphorylated at Ser-473 by CDK1 during mitosis, creating docking sites for the POLO box domains of PLK1. Subsequently, PLK1 binds and phosphorylates PPP1R12A (By similarity).