The kinetochore localization of Plk1 is regulated by deubiquitination and ubiquitination. The diagram shows that in early mitosis, cytosolic and possibly kinetochore-localized Usp16 is phosphorylated by CDK1 to generate a binding motif for PBD. A portion of preactivated Usp16 deubiquitinates Plk1 and promotes the binding of Plk1 to yet-to-be-identified kinetochore-localized proteins, which may include Usp16 as well, and the binding of Plk1 to cytosolic Usp16. Then, Plk1 further phosphorylates Usp16 to activate it. Usp16, in turn, keeps Plk1 in a deubiquitinated form and further enhances its binding to the kinetochore-localized proteins. By metaphase, CUL3 and substrate-specific adaptor KLHL22 become enriched at the kinetochores, which bind and ubiquitinate Plk1 within its PBD, resulting in the dissociation of Plk1 from its interacting proteins and the removal of Plk1 from the kinetochores. This allows the satisfaction of the spindle assembly checkpoint and subsequent chromosome separation. Question marks represent not-yet-identified kinetochore-localized proteins that may bind to Plk1. P, phosphorylation; Ub, ubiquitination.