Final answer:
ATM kinase is a protein kinase that recognizes DNA breaks and activates tumor suppressors such as p53 and Chk2.
Step-by-step explanation:
The protein kinase that can recognize double-strand DNA breaks and activate tumor suppressors such as p53 and Chk2 is ATM kinase. ATM kinase is activated by stress or DNA damage and phosphorylates Mdm2, causing it to dissociate from p53. It also phosphorylates Chk2 and p53. Once separated from Mdm2, phosphorylated p53 up-regulates several genes, including the p21 gene, which blocks the cell cycle between the G₁ and S, and G2-to-M phases.