Cyclins are a group of proteins used within the cell cycle. They form complexes with Cdk proteins and these complexes phosphorylate other proteins during control stages of the cell cycle. The synthesis of DNA and mitosis of eukaryotic cells are dependent on the formation of the Cyclin-Cdk complexes, without the formation of these complexes checkpoints cannot be passed within the cell cycle and cell division cannot occur .
Cyclins determine Substrate specificity and are a very diverse family of proteins (35 - 90 kDa).
There are several different cyclins within Mammals and they all bind to different Cdks:
- Cyclin D1-3 bind to Cdk 4 & Cdk 6 - present during G1
- Cyclin E binds to Cdk 2 - present at the Restriction Point
- Cyclin A binds to Cdk 2 - present during S phase
- Cyclin B binds to Cdk 1 - present during G2
- ↑ Protoplasma. 2001;216(3-4):119-42. Cyclin/Cdk complexes: their involvement in cell cycle progression and mitotic division. John PC, Mews M, Moore R. SourcePlant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia.