The contributions of proofreading and MMR to correcting base-base mismatches. Results on the left are for the pol2-exo- strains, and results on the right are for the pol3-exo- strains. The contributions of proofreading and MMR to correcting: (A) and (B) total base-base mismatches, (C) total C-dTTP mismatches (D) total G-dTTP mismatches, (E) individual C-dTTP mismatches at URA3 base pairs 345 and 679, and (F) individual G-dTTP mismatches at URA3 base pairs 368 and 764. The numbers superimposed within or above the pie slices indicate the error correction factors, either for proofreading (in blue) or MMR (in red).