{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Cyclins proteins regulate the progression of cells through the cell cycle, forming a complex with their partner, cyclin-dependent kinase (Cdk), which activates the latter’s protein kinase function. When its concentration is low, the cyclin detaches from the Cdk, inhibiting the enzyme’s activity. Cyclin D1 (or PRAD-1 or bcl-1) is a putative proto-oncogene, functioning in association with Cdk4 and/or Cdk6 by phosphorylating the Rb protein."}]}]}