Phosphorylates in vitro histone H3 at 'Ser-10' (H3S10ph) and 'Ser-28' (H3S28ph), but not at 'Thr-3' (H3T3ph) or 'Thr-11' (H3T11ph). Colocalizes with phosphorylated histone H3 during mitosis. Associates with cytoskeletal structures that are necessary for cytokinesis and with the microtubule spindle. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Inhibited by hesperadin. Cytoplasmic perinuclear region or in dots around the nucleolus and at the nuclear periphery in interphase cells, associated to centromeric regions of condensed chromosomes at metaphase and dispersed along the entire length of the chromosomes during anaphase (PubMed:16028112). Nucleus (PubMed:15722465). Abundant in roots, flowers and flower buds, low or absent in expanded leaves, stems and siliques. Expression peaks at mitosis. Phosphorylation at Thr-176 may regulate activity and degradation of AUR3 in a cell cycle dependent manner. Overexpression of AUR3 induces mitotic spindle defects, but the distribution of phosphorylation of histone H3 on the chromosome is not affected. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Aurora subfamily.