<P> Oxidized bases in DNA are produced in cells treated with Hoechst dye followed by micro-irradiation with 405 nm light . Such oxidized bases can be repaired by base excision repair . </P> <P> When the 405 nm light is focused along a narrow line within the nucleus of a cell, about 2.5 seconds after irradiation the chromatin remodeling enzyme Alc1 achieves half - maximum recruitment onto the irradiated micro-line . The line of chromatin that was irradiated then relaxes, expanding side - to - side over the next 60 seconds . </P> <P> Within 6 seconds of the irradiation with 405 nm light there is half - maximum recruitment of OGG1 to the irradiated line . OGG1 is an enzyme that removes the oxidative DNA damage 8 - oxo - dG from DNA . Removal of 8 - oxo - dG, during base excision repair, occurs with a half - life of 11 minutes . </P> <P> Ultraviolet (UV) light induces the formation of DNA damages including pyrimidine dimers (such as thymine dimers) and 6, 4 photoproducts . These types of "bulky" damages are repaired by nucleotide excision repair . </P>

A mutation which is the result of environmental factors damaging the dna