Balancing the kinetochore ledger

Reduction of polo-like kinase-1 (Plk1) at kinetochores as cells progress from prometaphase to metaphase is surprising given that the kinase is thought to stabilize kinetochore–microtubule (kt–MT) attachments. In this issue, Liu et al. (2012. J. Cell Biol. doi:10.1083/jcb.201205090) demonstrate that kinetochore-associated Plk1 is a potent suppressor of microtubule plus-end dynamics. The authors propose that Plk1 activity facilitates the establishment of kt–MT attachments in prometaphase by stabilizing microtubules and that reduction of the kinase in metaphase promotes force generation by dynamic microtubules.