The Use of DNA Glycosylases to Detect DNA Damage

Abstract

DNA glycosylases, first reported by Lindahl (1974), catalyze the scission of the glycosidic bond releasing damaged or mispaired bases as the first step of the base excision repair pathway (Fig. 12.1) (Dianov and Lindahl, 1994). Removal of damaged bases by a DNA glycosylase is generally associated with a specific type of damage (e.g., uracil-DNA glycosylase excises uracil bases formed by deamination or misincorporation into DNA; Lindahl, 1993). The specificity of DNA glycosylases, however, may also cross over to different types of DNA damage [e.g., AlkA protein, which excises a number of alkylated bases (Table I), also excises formyluracil and hydroxymethyluracil bases formed by oxidation (Bjelland et al., 1994)]. Proteins such as the uracil-DNA glycosylase, the AlkA protein, and the Tag protein leave abasic sites in DNA which are in turn processed by endonucleases cleaving the phosphodiester backbone hydrolytically at these sites (Dianov and Lindahl, 1994; Lloyd and Linn, 1993). In addition to this group of DNA glycosylases, the Fpg, Nth, and MutY proteins of E. coli and the UV endonuclease from bacteriophage T4 have physically associated activities incising DNA at abasic sites via β-elimination mechanisms (AP lyases) (Bailly and Verly, 1987; Gerlt, 1993), and as a consequence processing of these lesions may be slightly different than repair of abasic sites (Lloyd and Linn, 1993). The use of these enzymes in the detection of DNA damage is facilitated by the fact that DNA glycosylases are active in the presence of EDTA and function independent of any complex which may form in vivo. Table I summarizes several properties and damages recognized by DNA glycosylases.