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Basic steps of base excision repair. Base excision repair (BER) is a cellular mechanism, studied in the fields of biochemistry and genetics, that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome. The related nucleotide excision repair pathway repairs
The first column depicts mismatch repair in eukaryotes, while the second depicts repair in most bacteria. The third column shows mismatch repair, to be specific in E. coli. Micrograph showing loss of staining for MLH1 in colorectal adenocarcinoma in keeping with DNA mismatch repair (left of image) and benign colorectal mucosa (right of image).
Nucleotide excision repair is a DNA repair mechanism. [2] DNA damage occurs constantly because of chemicals (e.g. intercalating agents), radiation and other mutagens. Three excision repair pathways exist to repair single stranded DNA damage: Nucleotide excision repair (NER), base excision repair (BER), and DNA mismatch repair (MMR).
Base excision repair (BER): damaged single bases or nucleotides are most commonly repaired by removing the base or the nucleotide involved and then inserting the correct base or nucleotide. In base excision repair, a glycosylase [ 22 ] enzyme removes the damaged base from the DNA by cleaving the bond between the base and the deoxyribose.
The components of the system are MutS, which binds to the GT mismatch, the VSR endonuclease, which cuts the DNA, and MutL, which recruits the UvrD helicase. VSR (very short patch repair) endonucleases occur in a variety of bacteria. They work by cutting, or rather, making a nick in DNA if the base pair is mutated or damaged.
Apurinic/apyrimidinic (AP) endonuclease is an enzyme that is involved in the DNA base excision repair pathway (BER). Its main role in the repair of damaged or mismatched nucleotides in DNA is to create a nick in the phosphodiester backbone of the AP site created when DNA glycosylase removes the damaged base.
DNA mismatch repair (MMR) deficiency: The mismatch repair machinery recognizes and repairs erroneous base pair insertion, deletion or mis-incorporation. Enzymatic DNA editing Cytidine deaminase enzymes: This family of enzymes are part of the innate immune system and are involved in the control of retroviruses and transposons elements (including ...
Within DNA trinucleotide repeat sequences, the repair of DNA damage by the processes of homologous recombination, non-homologous end joining, DNA mismatch repair or base excision repair may involve strand slippage mispairing leading to trinucleotide repeat expansion when the repair is completed. [5]