photoreactive repair

Definition

Target type: biologicalprocess

The repair of UV-induced T-T, C-T and C-C dimers by directly reversing the damage to restore the original pyrimidines. [GOC:elh, PMID:10915863]

Photoreactive repair, also known as photoreactivation, is a light-dependent process used by many organisms, including bacteria, fungi, and some plants, to repair DNA damage caused by ultraviolet (UV) radiation. UV radiation can induce the formation of pyrimidine dimers, primarily cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs), within DNA. These dimers distort the DNA helix, preventing DNA replication and transcription, and potentially leading to mutations.

Photoreactive repair is catalyzed by photolyases, which are enzymes that bind to the damaged DNA and use energy from visible light, specifically in the 300-500 nm range, to break the covalent bonds of the pyrimidine dimers. Photolyases contain two chromophores: a pterin and a flavin adenine dinucleotide (FAD). The pterin chromophore absorbs the light energy, and transfers it to the FAD chromophore, which then catalyzes the breakage of the dimer bond.

The process begins with photolyase binding to the dimerized DNA site. Once bound, the photolyase absorbs light energy and transfers it to the FAD chromophore. The excited FAD then acts as a reducing agent to break the covalent bonds between the dimerized pyrimidines. This process restores the original, undamaged DNA structure, allowing for normal replication and transcription.

Photoreactive repair is an important mechanism for repairing DNA damage caused by UV radiation. However, it has limitations. It is only effective in organisms that possess photolyases, and it requires the presence of visible light. Moreover, it cannot repair all types of UV damage, such as those caused by thymine dimers. Other DNA repair mechanisms, such as nucleotide excision repair (NER), are needed to handle these types of damage.

Photoreactive repair is an essential process for life on Earth, as it protects organisms from the harmful effects of UV radiation. However, understanding the mechanisms of this repair process is also crucial for developing strategies to prevent and treat UV-induced skin cancer and other diseases.'
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