During nucleotide excision repair (NER), the UvrA•UvrB (AB) damage sensor identifies lesion-deformed DNA within a sea of undamaged DNA. We report the first structure of the AB sensor and of a novel UvrA conformer. In the structure of the AB sensor, a central UvrA dimer is flanked by two UvrB molecules, all linearly arrayed along a DNA path predicted by biochemical studies. DNA is predicted to bind to UvrA in the complex within a narrow and deep groove that is compatible with native duplex DNA only. In contrast, the shape of the corresponding surface in all other UvrA structures is wide and shallow and appears compatible with various types of lesion-deformed DNA. These differences point to conformation switching between the two forms as a component of the genome-scanning phase of damage sensing. We also show that the highly conserved signature domain II of UvrA, which is adjacent to the proximal nucleotide-binding site, mediates a critical nexus of contacts to UvrB and to DNA. Moreover, in the novel UvrA conformer, the disposition of this domain is altered such that association with either UvrB or DNA is precluded. Concomitantly, nucleotide is uniquely absent from the proximal binding site. Thus, the signature domain II is implicated in an ATP-hydrolysis-dependent conformational change that detaches UvrA from both UvrB and DNA after initial damage recognition. Finally, the disposition and number of UvrB molecules in the AB complex, both unanticipated, suggest that once UvrA departs, UvrB localizes to the site of damage by helicase-mediated tracking along the DNA. Together these results permit a high-resolution model for the dynamics of early stages in NER (1-6).

Research in the Jeruzalmi lab is supported by the NSF (MCB-0918161) and NIH (GM084162).

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