Peripheral Golgi protein GRASP65 is a target of mitotic polo-like kinase (Plk) and Cdc2.

Cell division is characterized by orchestrated events of chromosome segregation, distribution of cellular organelles, and the eventual partitioning and separation of the two daughter cells. Mitotic kinases, including polo-like kinases (Plk), influence multiple events in mitosis. In yeast two-hybrid screens using mammalian Plk C-terminal domain baits, we have identified Golgi peripheral protein GRASP65 (Golgi reassembly stacking protein of 65 kDa) as a Plk-binding protein. GRASP65 appears to function in the postmitotic reassembly of Golgi stacks. In this report we demonstrate binding between Plk and GRASP65 and provide in vitro and in vivo evidence that Plk is a GRASP65 kinase. Moreover, we show that Cdc2 can also phosphorylate GRASP65. In addition, we present data which support the observation that the conserved C terminus of Plk is important for its function. Deletion or frameshift mutations in the conserved C-terminal domain of Plk greatly diminish its ability to phosphorylate GRASP65. These and previous findings suggest that phosphorylation of Golgi components by mitotic kinases may regulate mechanisms of Golgi inheritance during cell division.