Fig. 3. Schiff base formation and the 5’dRP lyase activity of Polβ.

Schematic demonstrating the Schiff base formed as an intermediate in the 5’dRP lyase reaction conducted by Polβ, mediated by the nucleophile, K72. Completion of 5’dRP removal yields a final product (right side) that is further processed by Polβ by addition of a single nucleotide and ligation mediated by the XRCC1/LigIII heterodimer (see Fig. (1)). Evidence of the Schiff base is demonstrated by the stabilized DNA-protein complex formed upon reduction with NaBH₄ (bottom left).