ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer. Dimerizes through its coiled-coil domain. Autophosphorylated on serine and threonine residues. Belongs to the protein kinase superfamily. NEK Ser/Thr protein kinase family. NIMA subfamily.