Redoxy-endonuclease, an enzyme present in human and other cells, recognizes monobasic photoproducts that occur primarily at sites of cytosine following UV-irradiation of DNA at 254 nm. The wavelength dependence for formation of these photoproducts was determined using end-labeled DNA fragments of defined sequence irradiated with monochromatic light ranging from 254-360 nm as substrates for redoxy-endonuclease partially purified from HeLa cells. The base specificity and extent of DNA cleavage were determined by analysis of the enzyme-generated DNA scission products on DNA sequencing gels. Maximal incision at sites of cytosine and thymine was observed at 280 nm, suggesting that these photoproducts may be relevant with respect to the biological effects of solar radiation.

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