CDKs Associate with Cyclins at Specific Stages of the Cell

CDKs associate with cyclins at specific stages of the cell cycle.The CDK subunit is responsible for phosphorylating a substrate protein,while the cyclin is responsible for

A) progression into G₀.
B) degradation of the CDK after phosphorylation.
C) ubiquitin function.
D) dephosphorylating Rb.
E) determining which specific proteins will be phosphorylated.