May be involved in neuronal differentiation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CDK5. Predominantly perinuclear. Peripheral membrane protein. Expressed in brain, and, to a lower extent, in kidney, heart, lung and skeletal muscle. In the brain, expressed in the olfactory bulb, cerebellum, striatum, hippocampal formation, thalamus, hypothalamus, and pontine nuclei (at protein level). Isoform 2 is predominantly expressed in adult stage. Isoform 3 is up-regulated during postnatal development. Up-regulated during the apoptotic death of myeloid cells induced by cytokine withdrawal, such as IL3, and during G-CSF-induced terminal differentiation of myeloblasts to granulocytes. Autophosphorylated. Phosphorylated by CDK5 (By similarity). Belongs to the protein kinase superfamily. Tyr protein kinase family. Extended N-terminus.