Non-receptor serine/threonine protein kinase which is necessary for the maintenance of skeletal muscle structure and function. May play a role in myocyte differentiation and survival by regulating the integrity of the nuclear envelope and the expression of muscle-specific genes. May also phosphorylate PPP1R12A and inhibit the myosin phosphatase activity to regulate myosin phosphorylation. Also critical to the modulation of cardiac contractility and to the maintenance of proper cardiac conduction activity probably through the regulation of cellular calcium homeostasis. Phosphorylates PLN, a regulator of calcium pumps and may regulate sarcoplasmic reticulum calcium uptake in myocytes. May also phosphorylate FXYD1/PLM which is able to induce chloride currents. May also play a role in synaptic plasticity. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Coiled-coil-mediated oligomerization enhances the catalytic activity. Proteolytic processing of the C-terminus may release the protein from membranes and constitute a mean to regulate the enzyme. May be regulated by HSPB2, RAC1, RAF1 and G-protein second messengers (By similarity). Homodimer; homodimerization stimulates the kinase activity. Interacts with HSPB2; may enhance DMPK kinase activity. Interacts with PLN; phosphorylates PLN. May interact with RAC1; may regulate DMPK kinase activity. Interacts with LMNA; may regulate nuclear envelope stability (By similarity). Localizes to sarcoplasmic reticulum membranes of cardiomyocytes. Additional isoforms seem to exist. Expressed in all tissues tested, with a predominance in brain, skeletal muscle, heart, and other tissues containing smooth muscle. In the heart, expression is restricted to the cardiomyocytes in the ventricle and atrium. Primarily detected in striated muscle structures of the 14.5 day embryo, including all major muscles in the skeletal structures, cardiac muscle, diaphragm, and the smooth muscle of the lung and gut. The coiled coil domain is required for homodimerization and regulates the enzymatic activity. Phosphorylated. Autophosphorylates. Phosphorylation by RAF1 may result in activation of DMPK (By similarity). Proteolytic processing of the C-terminus may remove the transmembrane domain and release the kinase from membranes stimulating its activity. Mice are fertile and no negative selection against the absence of the protein is apparent. Newborn do not display hypotonia, respiratory distress or gross anatomical abnormalities. However, a progressive muscle weakness a hall mark of myopathies is observed. Muscles from mature mice show variation in fiber size, increase fiber degeneration and fibrosis. They also display age-related progression in atrioventricular conduction defects that are reminiscent of congenital myotonic dystrophy. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. DMPK subfamily.