 This relaxation allows other proteins in the nucleotide excision repair pathway to enter the chromatin and repair the DNA damaged by the UV-induced presence of cyclobutane pyrimidine dimers.In 2015, Zhu et al.showed that DDB2 down-regulates the acetylation of lysine 56 in histone H3 (H3K56Ac) after UV-induced DNA damage through DDB2 interaction with histone deacetylases 1 and 2.