Practice question

Despite proofreading, occasional mismatches escape locking before next polymerization step. Post-replicative mismatch repair scans daughter strand discriminated in E. coli by transient hemimethylation of GATC sites remaining unmethylated for minutes. MutS protein detects backbone distortion caused by mismatch, MutL coordinates endonuclease MutH cleavage of unmethylated nascent strand, and helicase plus exonucleases remove error-containing segment. Resynthesis by Pol III restores correct sequence using parental strand template. This pathway improves fidelity additional 100 to 1000-fold and explains hypermutator phenotype in MutSL deficient strains.