Serine/threonine-protein kinase that performs several important functions throughout M phase of the cell cycle, including the regulation of centrosome maturation and spindle assembly, the removal of cohesins from chromosome arms, the inactivation of anaphase-promoting complex/cyclosome (APC/C) inhibitors, and the regulation of mitotic exit and cytokinesis. Polo-like kinase proteins acts by binding and phosphorylating proteins are that already phosphorylated on a specific motif recognized by the POLO box domains. Phosphorylates cdc25, pkmyt1/myt1, stag2/sa2, tpx2. Plays multiple essential roles during mitosis. Phosphorylates the N-terminal domain of cdc25, which leads to cyclin b-cdc2 activation and mitotic entry. Also required for organization of bipolar spindles, and for exit from mitosis. Involved in kinetochore functions and sister chromatid cohesion by phosphorylating stag2/sa2. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation of Thr-201. Interacts with plk1 and kif2a. Interacts with fbxo5 (PubMed:17159919). localization at the centrosome starts at the G1/S transition (By similarity). Localized at centrosomes at prophase, spindles at metaphase, and at the midbody during cytokinesis. Localization to the centrosome is required for S phase progression (By similarity). By growth-stimulating agents. The POLO box domains act as phosphopeptide-binding module that recognize and bind serine-[phosphothreonine/phosphoserine]-(proline/X) motifs. plk1 recognizes and binds docking proteins that are already phosphorylated on these motifs, and then phosphorylates them (By similarity). Activated by phosphorylation on Thr-201 during M phase. Phosphorylated by stk10, leading to activation during oocyte maturation. Ubiquitinated by the anaphase promoting complex/cyclosome (APC/C) in anaphase and following DNA damage, leading to its degradation by the proteasome. Protein levels are down-regulated by proteasomal degradation in anaphase (By similarity). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.