Serine/threonine-protein kinase that phosphorylates histone H3 at 'Thr-3' (H3T3ph) during mitosis. May act through H3T3ph to both position and modulate activation of AURKB and other components of the chromosomal passenger complex (CPC) at centromeres to ensure proper chromatid cohesion, metaphase alignment and normal progression through the cell cycle. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Constitutive activity that does not require phosphorylation. Specifically inhibited by 3-(1H-indazol-5-yl)-N-propylimidazo[1,2-b]pyridazin-6-amine (CHR-6494). Nuclear during interphase and associates with the chromosomes and spindle apparatus during mitosis. Expressed in germ cells within the testis of adults and of embryos from day 24 onwards. Also present in adult thymus and weakly expressed in spleen, lung and whole embryo. Autophosphorylated on both serine and threonine residues (By similarity). Strongly phosphorylated during mitosis but this does not appear to significantly affect its intrinsic kinase activity. Phosphorylation by AURKB is required for full activity toward histone H3 at 'Ser-3' in mitosis (By similarity). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Haspin subfamily.