Final answer:
p53 is the protein that stalls cell cycle progression to enable DNA repair when damaged DNA is detected.
Step-by-step explanation:
The protein that stalls progression in order to repair DNA damage is p53. This multifunctional protein plays a critical role in maintaining the integrity of the genome by acting at the G₁ checkpoint of the cell cycle. When p53 detects damaged DNA in cells that are preparing to enter the S phase, it halts the cell cycle and facilitates the recruitment of repair enzymes. In case the DNA cannot be repaired, p53 can initiate apoptosis, preventing the duplication of damaged DNA. This function is essential for the prevention of mutations that could lead to cancer and other diseases.