Final answer:
Cell cycle MPF is composed of a cyclin-subunit and a kinase-active cyclin-dependent kinase (cdk). Together they form the active complex essential for cell cycle regulation, leading to cell division. This discovery was awarded the 2001 Nobel Prize in Physiology or Medicine.
Step-by-step explanation:
The Cell cycle MPF (maturation-promoting factor) contains a subunit with kinase activity, known as cyclin-dependent kinase (cdk), and a cyclin subunit. Cyclin is a regulatory polypeptide required for the activation of the CDK, which is responsible for phosphorylating other proteins to advance the cell through the cell cycle checkpoints. Levels of cyclin vary during the cell cycle, peaking in mitosis, while CDK levels remain relatively constant. Once bound together, the cyclin-CDK complex becomes fully active and can initiate the processes required for cell division. The importance of cyclin and CDKs in cell cycle regulation was recognized with the awarding of the 2001 Nobel Prize in Physiology or Medicine to Leland H. Hartwell, R. Timothy Hunt, and Paul M. Nurse.