AP endonuclease is an enzyme that plays a crucial role in the DNA repair process. It specifically recognizes and cleaves the phosphodiester bond at apurinic/apyrimidinic (AP) sites, which are locations in the DNA where a base has been lost. This action creates a break in the DNA strand, allowing for further repair mechanisms to take place. After the AP endonuclease makes its cut, other enzymes, such as DNA polymerase and DNA ligase, work to fill in the gap and restore the DNA to its original state. This repair process is essential for maintaining the integrity of the genetic material and preventing mutations.