Dimerization consists of the bonding of two monomers to form an oligomer, such as the formation of pyrimidine dimers as a result of exposure to UV radiation, which promotes the formation of a cyclobutyl ring between adjacent thymines in DNA. In human skin cells, thousands of dimers may be formed in a day due to normal exposure to sunlight. DNA polymerase η may help bypass these lesions in an error-free manner; however, individuals with defective DNA repair function, such as sufferers of xeroderma pigmentosum, are sensitive to sunlight and may be prone to skin cancer. Clinically, whether a tumor has formed as a direct consequence of UV radiation is discernible via DNA sequencing analysis for the characteristic context-specific dimerization pattern that occurs due to excessive exposure to sunlight.
