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 isoform 1 in G1/S-arrested cells. NEK2 isoform 2 is largely not present in the nucleolus, and does not appear to phosphorylate NEK11. Activated in response to DNA damage. Inhibited by zinc. Interacts with isoform 1 of NEK2. Nuclear during interphase but moves to the polar microtubules during prometaphase and metaphase (PubMed:12154088). Accumulates in the nucleolus in G1/S-arrested cells (PubMed:15161910). Poorly expressed in cerebellum, trachea, lung, appendix, and uterus. Predominantly expressed at S/G2/M phase. Phosphorylated by NEK2. Phosphorylation at Ser-273 is important for its activation. Belongs to the protein kinase superfamily. NEK Ser/Thr protein kinase family. NIMA subfamily. Truncated N-terminus.