DNA Damage by UV

Photocycloaddition and photoaddition provide good models for the mechanism by which ultraviolet light can cause damage to nucleic acids. When ultraviolet light damages DNA, the principal reactions occurring involve the nucleic acid bases. Photocycloaddition reactions to form 

Thymine and other bases in nucleic acids undergo dimerisation when irradiated with ultraviolet light, and this can result in DNA mutation or even cell death. 

The cyclobutane derivatives can revert to the original bases when irradiated with shorter-wavelength light. This reaction is involved in the repair process, which helps keep damage caused by ultraviolet to a minimum. Some repair mechanisms involve enzymes that are important in the breakdown of cyclobutane dimers by longer-wavelength light. 

Thymine also undergoes a photoaddition reaction with water to form the anti-Markovnikov product  

The reverse process, important in the repair process, occurs when the hydrate is irradiated with shorter-wavelength light. 

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In contrast to the direct induction of DNA damage by UV-C and UV-B light, UV-A produces damage indirectly through highly reactive chemical intermediates. Similar to ionizing radiation, UV-A generates... 

WEI H, CAO Q AND RAHN R o (1996) Inhibition of UV light- and Fenton reaction-induced oxidative DNA damage by the soybean isoflavone genistein. Carcinogenesis. 17 (1) 73-7. 

Kootstra A (1994) Protection from UV-B-induced DNA damage by flavanoids. Plant Mol Biol 26 771-774... 

Chen T, Greenberg MM (1998) Model studies indicate that copper phenanthroline induces direct strand breaks via (5-elimination of the 2 -deoxyribonolactone intermediate observed in ene-diyne mediated DNA damage. J Am Chem Soc 120 3815-3816 Chen T, Cook GP, Koppisch AT, Greenberg MM (2000) Investigation of the origin of the sequence selectivity for the 5-halo-2 -deoxyuridine sensitization of DNA to damage by UV-irradiation. J Am Chem Soc 122 3861-3866... 

There are two major types of DNA damage following UV radiation cyclobutane pyrimidine dimers (CPD) and pyrimidine-pyrimidone (6-4) photoproducts that are often simply called (6-4) photoproducts. Formation of these UV lesions may be influenced by the DNA sequence. Nevertheless, in general, CPDs are more abundant than (6-4) photoproducts in UV irradiated DNA. For example, in UVC-irradiated DNA, the overall ratio of CPDs to (6-4) photoproducts is about 3 1. 

Which of the following enzymes or processes can be involved in repairing DNA in E. coli damaged by UV-light-induced formation of a thymine dimer ... 

HlavataL, Bankova K, Vyskocil V, Labuda J (2012) Evaluation of damage to DNA induced by UV-C radiation and chemical agents using electrochemical biosensor based on low molecular weight DNA and screen-printed carbon electrode. Electrochim Acta 71 134-139. doi 10.1016/j.electacta.2012.03.119... 

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