Final answer:
p53 is the protein that is induced under cellular stress and sequesters MDM2 to regulate the cell cycle, particularly at the G1 checkpoint. It can induce the production of p21 and lead to cell cycle arrest or apoptosis in response to DNA damage.
Step-by-step explanation:
The question is asking about a protein that is induced under cellular stress such as oncogene activation and that sequesters MDM2. The correct answer is b) p53. p53 is widely known as a tumor suppressor protein and it plays a critical role in the cell cycle regulation. Under stress conditions, p53 levels increase, and this protein can trigger the production of p21 while also being responsible for holding the cell cycle at the G₁ checkpoint when there is DNA damage. p21, controlled by p53, inhibits the Cdk/cyclin complexes, thus enforcing the halt in the cell cycle dictated by p53. The sequestration of MDM2 by p53 helps in stabilizing p53 levels, contributing to cell cycle arrest and potentially leading to apoptosis if the damage is irreparable.