Proteins are known as what regulate the timing of the cell cycle in eukaryotic cells

Cyclin is a family of proteins that control the cell cycle. They undergo a cycle of synthesis and degradation in each cell cycle.Theyare divided into four classes. Three of these classes, G1/S cyclins, S cyclins, and M cyclins, are directly involved in the control of cell cycle events. The fourth class, the G1 cyclins, controls the entry into the cell cycle in response to extracellular growth factors.