Visual snapshots of intracellular kinase activity can be acquired with exquisite temporal control by using a light-activatable (caged) sensor, thereby providing a means to interrogate enzymatic activity at any point during the cell-division cycle. Robust protein kinase activity transpires just prior to, but not immediately after, nuclear envelope breakdown (NEB). Furthermore, kinase activity is required for the progression from prophase into metaphase. Finally, the application of selective protein kinase C (PKC)inhibitors, in combination with the caged sensor, correlates the action of the PKC � isoform with subsequent NEB.