Serine/threonine kinase involved in cell cycle, nuclear condensation and transcription regulation (PubMed:14645249, PubMed:18617507, PubMed:19103756). Involved in Golgi disassembly during the cell cycle: following phosphorylation by PLK3 during mitosis, required to induce Golgi fragmentation (PubMed:19103756). Phosphorylates 'Thr-18' of p53/TP53 and may thereby prevent the interaction between p53/TP53 and MDM2 (PubMed:10951572). 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 (PubMed:16495336). Phosphorylates ATF2 which activates its transcriptional activity (PubMed:15105425). 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+) (PubMed:11883897). Has a higher affinity for Mn(2+) than for Mg(2+) (PubMed:11883897). RAN inhibits its autophosphorylation and its ability to phosphorylate histone H3 (PubMed:18617507). (Microbial infection) Interacts with vaccinia protein B12; this interaction inhibits the repressive activity of the vaccinia virus B12 pseudokinase on viral replication factory formation. Dispersed throughout the cell but not located on mitotic spindle or chromatids during mitosis. Widely expressed. Highly expressed in fetal liver, testis and thymus. Autophosphorylated at various serine and threonine residues (PubMed:11883897, PubMed:14645249, PubMed:19103756, PubMed:21543316). Autophosphorylation does not impair its ability to phosphorylate p53/TP53 (PubMed:11883897). Phosphorylation by PLK3 leads to induction of Golgi fragmentation during mitosis (PubMed:19103756). The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. VRK subfamily.