Transitions through the cell cycle are driven by cyclins and cyclin-dependent kinases (CDKs) [PubMed: 26658964]. Cyclins are the allosteric activators of cognate CDKs; their levels typically oscillate across the cell cycle, hence gaining the name cyclins. . The cyclin family shares a homologous N-terminal 100-amino acid motif referred as the cyclin box that has a highly conserved three-dimensional structure and provides the binding interface for the appropriate CDKs [PubMed: 8591034]. D cyclins, including cyclins D1, D2 and D3, form active complexes with either CDK4 or CDK6, which in turn phosphorylate the retinoblastoma protein (Rb) and drive G1 to S phase progression [PubMed: 7505440].
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