Excision repair

Excision repair is a DNA repair mechanism that involves the removal of damaged or mismatched bases in the DNA molecule. This process is crucial for maintaining the integrity of the genetic material and preventing the accumulation of mutations that can lead to various diseases, including cancer.

Mechanism

The process of excision repair begins with the recognition of the damaged base by a specific DNA repair protein. This protein then recruits other proteins to the site of damage, forming a complex that facilitates the removal of the damaged base. The gap left by the excised base is then filled by a DNA polymerase, which uses the undamaged strand as a template to synthesize the correct base. Finally, the newly synthesized DNA is sealed by a DNA ligase, restoring the integrity of the DNA molecule.

There are two main types of excision repair: base excision repair (BER) and nucleotide excision repair (NER). In BER, the damaged base is removed by a specific DNA glycosylase, followed by the removal of the sugar-phosphate backbone by an AP endonuclease. In NER, a larger segment of DNA containing the damaged base is removed, and the gap is filled by a DNA polymerase.

Role in disease

Defects in excision repair can lead to a variety of diseases. For example, mutations in genes involved in NER can cause xeroderma pigmentosum, a rare genetic disorder characterized by extreme sensitivity to ultraviolet (UV) light and a high risk of skin cancer. Similarly, defects in BER can lead to various types of cancer and neurodegenerative diseases.

See also

• DNA repair
• Base excision repair
• Nucleotide excision repair
• Mismatch repair
• Direct repair