PROTEIN-KINASES IN THE CONTROL OF MITOSIS - FOCUS ON NUCLEOCYTOPLASMIC TRAFFICKING

The eukaryotic cell nucleus is a highly dynamic organelle. This is ill ustrated most dramatically during mitosis, when the nuclear envelope b reaks down, the nuclear lamina disassembles, chromosomes condense, and a microtubule-based spindle apparatus distributes sister chromatids t o the dividing daughter cells. Many of these dramatic changes in nucle ar architecture and microtubule organization are controlled by phospho rylation and dephosphorylation events. Whereas the cardinal role of cy clin-dependent kinases (CDKs) in the regulation of mitosis is well est ablished, there is now clear evidence for the requirement of additiona l mitotic protein kinases. Studies into the regulation of CDKs and oth er mitotic kinases have revealed that these enzymes undergo cell cycle dependent changes in subcellular distribution, suggesting that locali zation may contribute to regulating their activities. This article des cribes some recent findings relating to the nucleocytoplasmic transloc ation of CDK/cyclin complexes at the onset of mitosis, In addition, it summarizes recent information on two novel human protein kinases whic h have been implicated in the control of mitotic progression.