Pyrimidine-pyrimidone (6-4) photoproduct (6-4PP)

Pyrimidine-pyrimidone (6-4) photoproducts (6-4PPs) are a major class of DNA lesions caused by exposure to ultraviolet (UV) radiation, particularly UVB. They are formed by a photochemical reaction between two adjacent pyrimidines (thymine or cytosine), resulting in a covalent bond between the C6 position of the 5' base and the C4 position of the 3' base. Although they occur less frequently than cyclobutane pyrimidine dimers (CPDs), 6-4PPs cause significant structural distortion of the DNA helix, which typically allows them to be recognized and repaired more efficiently by the nucleotide excision repair (NER) pathway. If these lesions persist, they can lead to characteristic C-to-T transition mutations during DNA replication, which are primary drivers of skin cancers such as melanoma and non-melanoma skin cancers. Therapeutic strategies targeting 6-4PPs often involve the topical application of DNA repair enzymes, such as photolyases or T4 endonuclease V, to accelerate the removal of these lesions and reduce the risk of UV-induced malignancy.

Other names

6-4 photoproductPyrimidine-pyrimidone dimerUV-induced DNA lesion6-4 pyrimidine-pyrimidone photoproduct

Direct enzymatic repair of DNA lesions via nucleotide excision repair (NER) enhancement or direct reversal by exogenous DNA repair enzymes (e.g., photolyases) delivered topically to prevent mutagenesis and carcinogenesis.