Alternative excision repair pathways

Alternative excision repair (AER) is a category of excision repair initiated by a single nick, made by an endonuclease, near the site of DNA damage, and followed by excision of the damaged DNA, repair synthesis, and ligation. The ultraviolet (UV) damage endonuclease in fungi and bacteria introduces a nick immediately 5⁰ to various types of UV damage and initiates its excision repair that is independent of nucleotide excision repair (NER). Endo IV-type apurinic/apyrimidinic (AP) endonucleases from Escherichia coli and yeast and human Exo III-type APendonuclease APEX1 introduce a nick directly and immediately 5⁰ to various types of oxidative base damage besides the AP site, initiating excision repair. Another endo-nuclease, endonuclease V from bacteria o humans, binds deaminated bases and cleaves the phosphodiester bond located 1 nucleotide 3⁰ of the base, leading to excision repair. A single-strand break in DNA is one of the most frequent types of DNA damage within cells and is repaired efficiently. AER makes use of such repair capability f single-strand breaks, removes DNA damage, and has an important role in complementing BER and NER.