Action spectrum for the formation of endonuclease-sensitive sites and (6-4) photoproducts induced in a DNA fragment by ultraviolet radiation.

Using DNA sequencing techniques, action spectra were prepared for the site-specific induction of cyclobutane pyrimidine dimers and hot-alkali sites (probably mostly 5-hydroxy-6-4-(5'-methylpyrimidine-2'-one)-dihydrothymine) in a DNA of defined sequence. The spectra for the formation of two different photoproducts were indistinguishable from each other. However, the absolute rates of induction of dimers and hot-alkali sites were different from each other, and varied from site to site. At 254, 270, and 290 nm, the spectra correlate with the action spectrum of DNA. At longer wavelengths (313 and 334 nm), the action spectra diverge from the DNA spectrum, with the efficiency of formation of both photoproducts being greater than the DNA spectrum.