The activity of cyclin-dependent kinases (CDKs), following its name, is highly dependent on the attachment of cyclins. Cyclins are protein molecules whose concentration fluctuates throughout the whole cell cycle. With high cyclin concentration, CDKs also reach the optimum activity as MPF or M-phase promoting factor, named as such since its activity promotes the cell's entry to its M phase.
Which one of the following statements regarding the S cyclin-CDK complex is TRUE?
A. It is responsible for the phosphorylation of nuclear proteins.
B. It regulates the expression of histone proteins.
C. It ensures that DNA is not replicated multiple times.
D. It is responsible for the degradation of nuclear membranes.
E. It is regulated solely by the action of p53.