DNA repair is a phenomenal multi-enzyme, multi-pathway system required to ensure the integrity of the cellular genome. These cellular mechanisms that must cope with the plethora of DNA base pair adducts that arise.
DNA damage can arise spontaneously in the cellular milieu through chemical alteration of base nucleotides or as a consequence of errors during DNA replication. For example, it is well known that normal cellular pH and temperature offer an environment, which is hostile to the integrity of DNA and its nucleotide components. 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 DNA phosphate-sugar backbone.
The pioneering work from a number of laboratories have elucidated the basic mechanisms underlying distinct DNA repair pathways that include nucleotide excision repair (NER), base excision repair (BER), DNA strand break repair (DSBR), direct reversal of DNA damage, and the replication past DNA lesions by specialized DNA bypass polymerases (bypass replication). Defects in most of these repair pathways have been associated with one or more specific human diseases. Additionally, 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 as outlined herein.