Environmental factors can cause DNA damage. For example, UV light creates cyclobutane dimers (between two thymidine residues in DNA) that stall the progression of the replication machinery.
Abbreviations: cis-Pt and MMC, cisplatin and mitomycin C, respectively (both DNA-cross-linking agents); (6–4)PP and CPD, 6–4 photoproduct and cyclobutane pyrimidine dimer, respectively (both ...