Practice question

Overall replication fidelity in E. coli reflects three sequential filters acting in series. Base selectivity by Pol III active site contributes roughly 10^-5 error rate, proofreading by epsilon subunit adds 10^-2 improvement, and methyl-directed mismatch repair provides another 100 to 1000-fold correction. Combined outcome reaches one mistake per 10^9 to 10^10 nucleotides incorporated, equivalent to less than one error per genome duplication of 4.6 megabases. This extreme accuracy preserves genome stability despite rapid polymerization near 1000 nucleotides per second at each replication fork.