Serine/threonine-protein kinase involved in the control of mitotic transition and the regulation of cellular growth and/or development. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Autophosphorylates on tyrosine residues. Interacts with MDM2. Phosphorylated on serine/threonine residues. Phosphorylation on Thr-31 and Ser-367 by ATM in response to genotoxic stress disrupts MDM2 binding and prevents MDM2-mediated ubiquitination and subsequent proteasome degradation, thus promoting p53/TP53-mediated apoptosis (By similarity). Ubiquitination in nucleus by MDM2 in normal conditions leads to proteasome degradation. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. MNB/DYRK subfamily.