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I have investigated the effects of ultraviolet (UV) radiation on the overall structure of the closed circular DNA of simian virus 40 (SV40) and the influence of supercoiling upon these effects. The lesions produced in highest yield at biologically significant fluences of UV radiation are cyclobutane-type pyrimidine dimers (Yang 1976). X-ray diffraction data (Camerman and Camerman 1968) show a 6° reduction in the twisting angle between the two thymine bases as well as an alteration in the angle between the planes of the adjacent bases in the cis-syn cyclobutane thymine dimer. Such alterations distort the DNA double helix and might influence its overall behavior.
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Howard J. Edenberg (1983) studied this question.
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