Excision of products of oxidative DNA base damage by human NTH1 protein

A functional human homologue of Escherichia coli endonuclease III (nth-Eco protein) has recently been cloned and characterized [Aspinwall, R., Rothwel l, D. G., Roldan-Arjona, T., Anselmino, C., Ward, C. J., Cheadle, J. P., Sa mpson, J. R., Lindahl, T., Harris, P. C., and Hickson, I. D. (1997) Proc. N atl. Acad. Sci. U.S.A., 94, 109-114]. This enzyme, designated hNTH1 protein , shares an extensive sequence similarity with Nth-Eco protein and a relate d enzyme from Schizosaccharomyces pombe (Nth-Spo protein). We investigated the substrate specificity of this human enzyme for oxidative DNA base damag e, using the technique of gas chromatography/isotope-dilution mass spectrom etry. Four different DNA substrates damaged by various free radical-generat ing systems were used. 5-Hydroxycytosine, thymine glycol, 5-hydroxy-6-hydro thymine, 5,6-dihydroxycytosine, and 5-hydroxyuracil were substrates of hNTH 1 protein among 17 lesions found in DNA substrates. The substrate specifici ty and excision kinetics of the human enzyme were found to be significantly different from those of Nth-Spo and Nth-Eco proteins.