DNA repair is required to maintain the integrity of the cellular genome in the face of DNA damage that arises spontaneously in the cellular milieu through chemical alteration of base nucleotides or as a consequence of errors during DNA replication. Additionally, DNA damage may be induced in response to environmental exposures, including exposure to physical agents such as ionizing or ultraviolet (UV) radiation. Finally, specific chemical agents are known to alkylate or cross-link DNA bases, produce bulky adducts on DNA bases, or break the DNA phosphate-sugar backbone.
Distinct DNA repair pathways include nucleotide excision repair (NER), base excision repair (BER), DNA strand break repair (DSBR), direct reversal of DNA damage, and replication past DNA lesions by specialized DNA bypass polymerases (bypass replication). The repair of damaged DNA is intimately associated with a number of other distinct cellular processes such as DNA replication, DNA recombination, cell cycle checkpoint arrest, and other basic cellular mechanisms.