Rapid Report FIGURE 4: Levels of 8-OH-Gua in liver DNA of wild-type (1) (n = 4), neil1-/- (2) (n = 8), and ogg1-/- (3) (n = 8) mice. The uncertainties are standard deviations. *p < 0.05. hand, NEIL1 may also interact with other proteins of the NER complex. Since NEIL1 is not capable of initiating BER at these lesions, it may be possible that it binds to them and accelerates the repair that is normally initiated through NER. Previously, the binding of DNA photolyase to cyclobutane pyrimidine dimers under noncatalytic conditions was shown to facilitate the effi- ciency of repair via the E. coli UvrABC complex (27, 28). These data revealed the principle that DNA lesions can be non- covalently bound by proteins, thereby facilitating their ultimate repair. Whatever the mechanism of action of NEIL1 is in NER, we propose that NEIL1 is involved in NER of R-cdA and S-cdA, and perhaps other complex lesions not subject to BER. NEIL1 may act with CSB and/or any other NER proteins in this process. 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