Figure 4. Conceptual representation of mutation avoidance by BER during nitrosative stress.

NO· can be oxidized to nitrous anhydride (N₂O₃) and/or peroxynitrite (ONOO⁻) depending in the presence or absence of superoxide. Nitrous anhydride and peroxynitrite mediate DNA base deamination and oxidation, respectively. The Ung repair pathway removes dU from DNA via an AP site, thereby avoiding the MUTATION pathway. Similarly, Fpg removes oxidized dG, limiting peroxynitrite-mediated hypermutation, but increased mutability in cells lacking Fpg can be ameliorated by MutY. NO·-induced mutations can also be avoided by pathways that do not produce AP site intermediates (e.g., Nfi).