Mutations in the gene encoding the alpha subunit of pol III are known which cause higher or lower rates of misincorporation. These affect selectivity of the incoming triphosphate. Mismatch Repair by the MutHLS methyl-directed repair system. MutL binds to the complex with MutH . MutH is an endonuclease that binds to GATC sequences and cuts the unmethylated strand of hemimethylated GATC sequences in DNA near the mismatch.
Exonucleases remove the unmethylated strand past the mismatch.
SSB binds the single strands which are filled in by the action of DNA pol III, and sealed by ligase. This system uses the methylation state of the DNA to determine which strand is the older one, on the assumption that the mismatch it detects is caused by misincorporation during replication, and that the older strand should be used as a template for repair. In dam - mutants, either strand can be selected as the template for repair. Mutations in the human homologs of MutH are implicated in certain hereditary cancers. Repair of Spontaneous Cytidine deamination.