Serine/threonine kinase involved in cell cycle, nuclear condensation and transcription regulation (PubMed:14645249, PubMed:9521809, PubMed:33076429). Involved in Golgi disassembly during the cell cycle: following phosphorylation by PLK3 during mitosis, required to induce Golgi fragmentation (By similarity). Phosphorylates 'Thr-18' of p53/TP53 and may thereby prevent the interaction between p53/TP53 and MDM2 (By similarity). Phosphorylates KAT5 in response to DNA damage, promoting KAT5 association with chromatin and histone acetyltransferase activity (PubMed:33076429). Phosphorylates BANF1: disrupts its ability to bind DNA, reduces its binding to LEM domain-containing proteins and causes its relocalization from the nucleus to the cytoplasm (By similarity). Phosphorylates ATF2 which activates its transcriptional activity (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Active in presence of Mn(2+), Mg(2+) and Zn(2+), but is not functional with Ca(2+) or Cu(2+). Has a higher affinity for Mn(2+) than for Mg(2+). RAN inhibits its autophosphorylation and its ability to phosphorylate histone H3 (By similarity). Dispersed throughout the cell but not located on mitotic spindle or chromatids during mitosis. Highly expressed in testis. Expressed in liver, kidney and muscle. Weakly expressed in thymus, bone marrow and spleen. Expressed from 10.5 dpc to 14 dpc in developing liver and then decreases. It increases again from 17.5 dpc and remains thereafter. Highly expressed in hematopoietic embryonic tissues from 10.5 dpc to 14.5 dpc. Weakly expressed in the yolk-sac. Autophosphorylated at various serine and threonine residues (PubMed:14645249). Autophosphorylation does not impair its ability to phosphorylate p53/TP53 (By similarity). Phosphorylation by PLK3 leads to induction of Golgi fragmentation during mitosis (By similarity). Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. VRK subfamily.