Practice question

In Escherichia coli, adenine in GATC sequences is methylated by Dam methylase on both strands. Immediately after replication fork passage, parental template remains fully methylated while nascent daughter strand is transiently unmethylated, generating hemimethylated duplexes. MutS scans DNA for mismatches and recruits MutL, which activates latent endonuclease activity of MutH. Recognition of hemimethylated GATC provides temporal strand discrimination signal. MutH selectively nicks unmethylated daughter strand 5' to G, creating entry for UvrD helicase and exonucleases to excise error-containing segment and preserve template fidelity.