Why are cyclins expressed at different times and at different levels during the cell cycle?
One or more cyclins must interact with each other to control the cell cycle.
Cyclins are transcription factors responsible for the expression of crucial cell-cycle proteins.
Cyclins are involved in arresting the cell cycle. Removal of certain cyclins allows the cell cycle to proceed.
Different cyclins combine with protein kinases at different stages of the cell cycle to affect the cell cycle.