How do DNA-repair enzymes find aberrant nucleotides among the myriad of normal ones? One enzyme has been caught in the act of checking for damage, providing clues to its quality-control process. DNA-repair enzymes amaze us with their ability to searchthrough vast tracts of DNA to find subtle anomalies in the structure. The human repair enzyme 8-oxoguanine glycosylase (hOGGl) is particularly impressive in this regard because it efficiently removes 8-oxoguanine (oxoG), a damaged guanine (G) base containing an extra oxygen atom, and ignores undamaged bases. Verdine and colleagues now report the structure of hOGGl bound to undamaged DNA (Banerjee et al., page 612 of this issue), revealing a unique strategy that allows faithful removal of damaged basesbut not their normal counterparts.
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