What process triggers repair for pyrimidine dimers formed by UV light?

Pyrimidine dimers, such as thymine dimers, are formed when UV light induces covalent bonding between adjacent thymine bases in DNA, disrupting normal base pairing and leading to potential mutations. Photoreactivation is a specific DNA repair process that directly reverses this type of damage caused by UV radiation.

This process utilizes the enzyme photolyase, which binds to the pyrimidine dimer and, upon absorbing visible light, catalyzes the cleavage of the bonds between the dimerized bases, restoring them to their original state without removing any DNA nucleotides. Photoreactivation is particularly efficient and is found in many organisms, including bacteria and some plants.

This mechanism contrasts with other forms of DNA repair. Excision repair usually involves the removal of a segment of DNA surrounding a damaged region before synthesizing a new DNA segment to fill the gap. Base pairing repair is not a recognized terminology commonly associated with DNA repair mechanisms. Homologous recombination typically refers to the repair of double-strand breaks rather than specific lesions like pyrimidine dimers. Therefore, photoreactivation is the most direct and effective response to repair pyrimidine dimers, reflecting the specialized nature of DNA damage caused by UV light.