Sequential activation of members of the cyclin-dependent protein kinase (CDK) family promotes the correct timing and ordering of events required for cell growth and cell division . In addition to driving progress through the cell cycle, CDKs are also the downstream targets of checkpoint pathways. These checkpoints act to ensure that critical cell cycle events have been successfully completed before the cell progresses into the next cell cycle stage. They are composed of a surveillance system that detects when a particular cell cycle event has not been correctly executed and a signal transduction pathway whose ultimate target can be a CDK.
Monomeric CDKs are inactive and require both association with a positive regulatory subunit, called a cyclin, and phosphorylation on a conserved threonine residue that lies within the activation loop for full activity. Both the CDK and cyclin families have multiple members, but only CDKs 1, 2, 4 and 6, when bound to their cognate cyclins, appear to have major roles in controlling cell cycle progression. These CDK/cyclin complexes are then additionally controlled by mechanisms that include inhibitory phosphorylation, protein association, subcellular localisation and targeted destruction of regulatory proteins.
Monomeric CDKs are inactive and require both association with a positive regulatory subunit, called a cyclin, and phosphorylation on a conserved threonine residue that lies within the activation loop for full activity. Both the CDK and cyclin families have multiple members, but only CDKs 1, 2, 4 and 6, when bound to their cognate cyclins, appear to have major roles in controlling cell cycle progression. These CDK/cyclin complexes are then additionally controlled by mechanisms that include inhibitory phosphorylation, protein association, subcellular localisation and targeted destruction of regulatory proteins.
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