Interactions among Dam, SeqA and mismatch repair proteins in Escherichia coli

The accuracy of DNA replication is very important, and organisms have several proofreading and repair systems to prevent mutations from occurring. Lesions can be introduced by errors during replication, chemical mutagens, UV or ionizing radiation. In Escherichia coli, mismatches are detected by MutS and MutL which together activate MutH to initiate repair. Repair is dependent on GATC hemi-methylation signals on the DNA which is added by DNA adenosine methylase (Dam). SeqA acts as a regulator of DNA replication, sequestering the origin and preventing reinitiation. We hypothesize that 1) Dam and SeqA are coordinated by MutL, and (2) persistent mismatches caused by lack of polymerase proofreading will increase mismatch repair activity. Results show that Dam binds to both SeqA and MutL, and no significant increase in mismatch repair activity was detected when the error prone polymerase was induced. These data suggest the importance of temporal coordination of methylation and/or interaction of Dam and MutL in preparation for mismatch repair. Our data is consistent with previous literature that shows mismatch repair primarily works against transitions and is inefficient at preventing transversions.