In the diagram above, notice that cyclin levels CYCLE (get the name now?), and MPF (maturation promoting factor, a specific name of a cyclin/CDK complex) follows the same pattern. When cyclin levels are high, MPF activity is high, and vice versa. The height of activity peaks at M phase. This tells us that the role of this active complex is to move through M phase, and then cyclin levels, and MPF activity levels, drop off quickly after that.