Which regulatory protein is present in all stages of the cell cycle but has varying degrees of phosphorylation (activation) from phase to phase?
A) p53
B) Rb protein
C) p21
D) Cyclin D

Question

Quizplus · Accepted Answer

The Rb protein is present in all stages of the cell cycle but has varying degrees of phosphorylation (activation) from phase to phase. During the G1 phase, Rb is unphosphorylated and acts as a tumor suppressor by binding to and inhibiting the E2F transcription factor. In S phase, Rb is phosphorylated by Cyclin D and CDK4/6, allowing for the release of E2F and progression of the cell cycle. In G2 and M phases, Rb becomes dephosphorylated and can once again inhibit E2F, ensuring proper progression through the cell cycle.

Which Regulatory Protein Is Present in All Stages of the Cell