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MMR in Escherichia coli strain K-12 substr. MG1655
MMR in KEGG: eco03430
DNA mismatch repair (MMR) is responsible for correction of replication errors (mismatches and small insertions and deletions) that escape the proofreading activity of a DNA polymerase.
In E. coli, MMR is initiated by MutS, MutL, and MutH. MutS first recognizes the error in DNA, and then physically interact with MutL, which next activates other proteins that remove the error-bearing DNA strand and synthesize the new one.
In Escherichia coli and closely related γ-proteobacteria, MMR is dependent on hemimethylated GATC sites, which are used for discriminating between parental and daughter DNA strands (the daughter strand is transiently unmethylated shortly after replication).
The actual DNA repair in MMR is initiated by a nick in GATC site that can be either 5' or 3' to the mismatch. Thus, both 5'- and 3'-directed paths have been included in this pathway.
The mechanism of the MMR proposed below assumes that MutS-MutL complex remains bound to the mismatch when MutH is activated but it is also possible that the MutS-MutL-MutH leave the mismatch to search for GATC sites. It is also uncertain when MutS, MutL, and MutH dissociate from each other.