function that helps activate other enzymes involved in DNA repair. As such, knocking down APE1 could lead to tumor cell sensitivity, thus preventing cancer cells from persisting after chemotherapy. APE2 enzyme activity APE2 has much weaker AP endonuclease activity than APE1, but its 3'-5' exonuclease activity is strong compared with APE1 and it has a fairly strong 3'-phosphodiesterase activity. The APE2 3' –5' exonuclease activity has the ability to hydrolyze blunt-ended duplex DNA, partial DNA duplexes with a recessed 3' -terminus or a single nucleotide gap containing heteroduplex DNA. The APE2 3'-phosphodiesterase activity can remove modified 3'-termini, such as 3'-phosphoglycolate as well as mismatched nucleotides from the 3' primer end of DNA. APE2 is required for ATR-Chk1 DNA damage response following oxidative stress. References Molecular graphics images were produced using the UCSF Chimera package from the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco (supported by NIH P41 RR-01081). External links Basic Definition of AP endonuclease AP endonucleases family 1 in PROSITE AP endonucleases family 2 in PROSITE Application in Long Patch Base Excision Repair Purification and characterization of an apurinic/apyrimidinic endonuclease from HeLa cells Enzymes