Inactive serine/threonine-protein kinase that plays a role in cell cycle progression and neuronal differentiation. Expressed in the cerebellum, eye and brain cortex (at protein level). Expressed in highly differentiated tissues, such as brain, eyes and ovary. Not detectable in proliferating tissues, such as the colon, spleen and placenta. Down-regulated in proliferating cells or in serum-stimulated cells or growth factors. Up-regulated in asynchronous cells, or upon serum deprivation or following stress inducible DNA damage treatment. The protein kinase domain is predicted to be catalytically inactive; has lost the main activatory autophosphorylation site and the conserved key residues involved in phospho-substrate. The C-terminal region (containing the POLO box domain) is sufficient for inducing cell cycle arrest (By similarity). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDC5/Polo subfamily. Truncated N-terminus.