Mutagenic effect of radiation

All these bases absorb around 260 nm. Thymine and cytosine are most sensitive to irradiation. Two most important types of photochemical reactions that have been observed for these pyrimidine bases are photohydration and photodimerization. In vivo systems, interactions between protons and nucleic acids can also be initiated by radiations of wavelength dlorter than 300 nm. 

E Photodimerization occurs between pyrimidine bases when they are Packed in suitable geometry in the helical DNA molecule. Thymine is tost susceptible to photodimerization which occurs at A 280 nm. The 

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This stage has also shown no mutagenic effect of radiation. 

There is strong experimental and epidemiologic evidence linking UV radiation to the development of skin cancers (recently reviewed by Holmquist and Gao, 1997). p53 mutations are common in all skin cancers except melanoma, in which p53 appears to be inactivated by alternative, unknown mechanisms. The p53 mutation spectrum in nonmelanoma skin cancers (NMSC) shows a high frequency of C to T transitions (56% of all mutations), including tandem CC to TT transitions (6% of all mutations), a type of mutation that is extremely uncommon in any other tumor type. Both types of mutation are consistent with the mutagenic effects of UV in vitro. In particular, tandem CC to TT mutations are formed as a result of inefficient repair of a common photoproduct, cyclobutane pyrimidine dimers. 

R. B. Webb, Lethal and mutagenic effects of near-ultraviolet radiation, Photochem. Photobiol. Rev. 2, 169-261 (1977). 

Comparison of the Mutagenic Effect of Ultraviolet Radiation and Chemicals in Normal and DNA-Repair-Deficient Human Cells in Culture... 

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