Serine/threonine-protein kinase involved in cell cycle regulation, response to stress and Golgi disassembly. Polo-like kinases act by binding and phosphorylating proteins that are already phosphorylated on a specific motif recognized by the POLO box domains. Phosphorylates ATF2, BCL2L1, CDC25A, CDC25C, CHEK2, HIF1A, JUN, p53/TP53, p73/TP73, PTEN, TOP2A and VRK1. Involved in cell cycle regulation: required for entry into S phase and cytokinesis. Phosphorylates BCL2L1, leading to regulate the G2 checkpoint and progression to cytokinesis during mitosis. Plays a key role in response to stress: rapidly activated upon stress stimulation, such as ionizing radiation, reactive oxygen species (ROS), hyperosmotic stress, UV irradiation and hypoxia. Involved in DNA damage response and G1/S transition checkpoint by phosphorylating CDC25A, p53/TP53 and p73/TP73. Phosphorylates p53/TP53 in response to reactive oxygen species (ROS), thereby promoting p53/TP53-mediated apoptosis. Phosphorylates CHEK2 in response to DNA damage, promoting the G2/M transition checkpoint. Phosphorylates the transcription factor p73/TP73 in response to DNA damage, leading to inhibit p73/TP73-mediated transcriptional activation and pro-apoptotic functions. Phosphorylates HIF1A and JUN is response to hypoxia. Phosphorylates ATF2 following hyperosmotic stress in corneal epithelium. Also involved in Golgi disassembly during the cell cycle: part of a MEK1/MAP2K1-dependent pathway that induces Golgi fragmentation during mitosis by mediating phosphorylation of VRK1. May participate in endomitotic cell cycle, a form of mitosis in which both karyokinesis and cytokinesis are interrupted and is a hallmark of megakaryocyte differentiation, via its interaction with CIB1. {ECO:0000269|PubMed:10557092, ECO:0000269|PubMed:11156373, ECO:0000269|PubMed:11447225, ECO:0000269|PubMed:11551930, ECO:0000269|PubMed:11971976, ECO:0000269|PubMed:12242661, ECO:0000269|PubMed:14968113, ECO:0000269|PubMed:14980500, ECO:0000269|PubMed:15021912, ECO:0000269|PubMed:16478733, ECO:0000269|PubMed:16481012, ECO:0000269|PubMed:17264206, ECO:0000269|PubMed:17804415, ECO:0000269|PubMed:18062778, ECO:0000269|PubMed:18650425, ECO:0000269|PubMed:19103756, ECO:0000269|PubMed:19490146, ECO:0000269|PubMed:20889502, ECO:0000269|PubMed:20940307, ECO:0000269|PubMed:20951827, ECO:0000269|PubMed:21098032, ECO:0000269|PubMed:21264284, ECO:0000269|PubMed:21376736, ECO:0000269|PubMed:21840391, ECO:0000269|PubMed:9353331}. This is the function of Ensembl gene identifier ENSG00000173846 (PLK3, polo like kinase 3).