Oxidative base damage to DNA: specificity of base excision repair enzymes

Base excision repair (BER) is Likely to be the main mechanism involved in t he enzymatic restoration of oxidative base lesions within the DNA of both p rokaryotic and eukaryotic cells. Emphasis was placed in early studies on th e determination of the ability of several bacterial DNA N-glycosylases, inc luding Escherichia coli endonuclease III (endo III) and formamidopyrimidine DNA N-glycosylase (Fpg), to recognize and excise several oxidized pyrimidi ne and purine bases. More recently, the availability of related DNA repair enzymes from yeast and human has provided new insights into the enzymatic r emoval of several OH-mediated modified DNA bases. However, it should be not ed that most of the earlier studies have involved globally modified DNA as the substrates. This explains. at least partly, why there is a paucity of a ccurate kinetic data on the excision rate of most of the modified bases. In terestingly, several oxidized pyrimidine and purine nucleosides have been r ecently inserted into defined sequence oligonucleotides. The use of the lat ter substrates, together with overexpressed DNA N-glycosylases, allows deta iled studies on the efficiency of the enzymatic release of the modified bas es. This was facilitated by the development of accurate chromatographic and mass spectrometric methods aimed at measuring oxidized bases and nucleosid es. As one of the main conclusions, it appears that the specificity of both endo III and Fpg proteins is much broader than expected a few years ago. ( C) 2000 Elsevier Science B.V. All rights reserved.