AP endonucleases

From Wikipedia, the free encyclopedia

An AP endonuclease is an enzyme that cuts a strand of DNA on the 5'-side of an AP (apurinic/apyrimidinic) site, as part of DNA base excision repair (BER). Mg²⁺ is required for activity.

[edit] Mechanism

First DNA glycosylases recognize and excise the damaged bases from the sugar phosphate backbone of the DNA. It does this by cleaving the N-glycosylic bond between the target base and deoxyribose. What is left is an abasic site (or AP,apurinic/aprimidinic). The group of enzymes called AP-endonucleases recognize the abasic site and make an incision at the 5' or 3' phosphodiester of the AP site which generates a nucleotide gap. It is then filled by polmerization (DNA polymerase I) and ligation (DNA ligase) of the new nucleotide to the existing DNA sequence.AP endonucleases is also called as molecular scissors.