Description
Polo-like kinases (Plk) have been shown to be important contributors to several cell-cycle events. Genetic and biochemical experiments in various organisms indicate that polo-like kinases regulate diverse cellular events at multiple mitotic stages. Genetic studies in Drosophila and yeast indicate plks function in centrosome assembly and separation during the formation of the bipolar spindle. Drosophila polo mutants reveal phenotypes of hyper-condensed chromosomes, monopolar spindles, disorganized spindle poles, and abnormal chromosome segregation. Schizosaccharomyces pombe plo1 displays similar phenotypes, such as the formation of monopolar spindles or a failure in septum formation after nuclear division. The budding yeast polo-like kinase homolog, Cdc5, seems to play an important role in actin ring formation and cytokinesis. In mammalian cells, antibody microinjection suggests a role for Plk1 in centrosome maturation. Mammalian Plk1 was further shown to phosphorylate specifically at least three components of APC, and to activate APC to ubiquitinate cyclin B in an in vitro-reconstituted system. More recent studies demonstrated that polo kinase activity plays a pivotal role in the separation of sister chromatids during mitosis