Protein kinase which plays an important role in the G2/M checkpoint response to DNA damage. Controls degradation of CDC25A by directly phosphorylating it on residues whose phosphorylation is required for BTRC-mediated polyubiquitination and degradation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Autorepressed by intramolecular binding of the C-terminus which dissociates following phosphorylation by NEK2. Activated in response to DNA damage. Inhibited by zinc. Interacts with NEK2. Nuclear during interphase but moves to the polar microtubules during prometaphase and metaphase. Accumulates in the nucleolus in G1/S-arrested cells. Phosphorylated by NEK2. Phosphorylation at Ser-274 is important for its activation. Belongs to the protein kinase superfamily. NEK Ser/Thr protein kinase family. NIMA subfamily.