Excision repair

Excision repair is a term applied to several DNA repair mechanisms.

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Excision repair mechanisms that remove the damaged nucleotide replacing it with an undamaged nucleotide complementary to the nucleotide in the undamaged DNA strand. These include:

• Base excision repair (BER), which repairs damage due to a single nucleotide caused by oxidation, alkylation, hydrolysis, or deamination;
• Nucleotide excision repair (NER), which repairs damage affecting 2−30 nucleotide-length strands. These include bulky, helix distorting damage, such as thymine dimerization and other types of cyclobutyl dimerization caused by UV light as well as single-strand breaks. A specialized form of NER known as Transcription-Coupled Repair (TCR) deploys high-priority NER repair enzymes to genes that are being actively transcribed;
• Mismatch repair (MMR), which corrects errors of DNA replication and recombination that result in mispaired nucleotides.