PHOTOCHEMISTRY OF DNA USING 193 nm EXCIMER LASER RADIATION

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Abstract
Photoproducts in double‐stranded DNA induced by 193 nm radiation have been investigated. Double‐stranded, supercoiled pBR322 DNA in buffered aqueous solution was exposed to varying fluences of 193 nm radiation from an ArF excimer laser. The quantum yields for formation of cyclobutylpyrimidine dimers, frank strand breaks and alkali labile sites were calculated from the conversion of supercoiled (Form I) DNA to relaxed (Form II) DNA after treatment withMicrococcus luteusdimer‐specific endonuclease, no treatment, or treatment with alkali and heat, respectively. The quantum yields were 1.65 (± 0.03) × 10−3for pyrimidine dimers, 9.4 (± 3.2) × 10−5for frank strand breaks and 9.6 (± 3.6) × 10−5for alkali labile sites. The quantum yields for pyrimidine dimers and frank strand breaks were independent of Tris buffer and EDTA concentrations. The yields of frank strand breaks and alkali labile sites were not affected by 10mMmannitol. The relative quantum yields for these DNA photoproducts induced by 193 nm radiation differed markedly from those produced by 254 nm radiation.