Types of Damage Repaired by BER

As mentioned above, a wide variety of damaged DNA bases result from the attack of various environmental agents (Table I). The enormous molar excess of water ( 55 M) over the genome provides driving force for water to cause hydrolytic deamination of amine-containing DNA bases. The 

Source of damage Example lesion Responsible DNA glycosylases 

The most well-known form of ultraviolet light—induced base damage is the pyrimidine dimer. Although the hallmark repair system for this type of 

DNA lesion is NER, the BER response is also known to process cyclobutane thymine dimers (Seawell et al., 1980). 

An experimentally useful feature of the bifunctional mechanism is the capability of reducing agent (i.e., NaBH4) to intercept the covalent enzyme-DNA intermediate (Dodson etal, 1994 Nash etal, 1996 Sun etal, 1995). The result of reduction is a covalent single bond between the glycosylase and substrate DNA that is quite stable (Fig. 2, structure 5). This borohydride trapping procedure has been useful in the isolation (Bruner et al, 1998 Nash et al, 1996 Piersen et al, 1995) and characterization (Girard et al, 1997 Ikeda et al, 1998 Nash et al, 1997 Sidorkina 

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