Master controllers of this process include the cyclins, which regulate cyclin-dependent kinase or CDK. Recall that kinases are proteins that phosphorylate other proteins. CDK’s phosphorylation of its targets allows mitosis to proceed. To be precise, the maturation promoting factor or MPF is an obligate heterodimeric complex composed of cyclin B and CDK, which only does its phosphorylating action when both proteins are present.
