DNA polymerase is a crucial protein in DNA replication. However, it is not immune to making errors during the process. To safeguard against these errors, two proofreading mechanisms are employed.
1). Exonuclease Activity:
Certain DNA polymerase proteins possess exonuclease activity, which enables them to "proofread" the newly synthesized DNA strand. As the polymerase moves along the template strand, it checks each added nucleotide for accuracy. If an incorrect nucleotide is detected, the exonuclease activity of the polymerase removes it, allowing the correct nucleotide to be inserted. This editing mechanism helps to maintain the fidelity of DNA replication.
2). Post-replicative Mismatch Repair:
In addition to the exonuclease proofreading activity of DNA polymerase, cells have an additional "post-replicative mismatch repair" mechanism. This system utilizes proteins such as MutS and MutL to scan the newly synthesized DNA strand for any mismatched nucleotides. Once a mismatch is identified, the MutH protein nicks the DNA strand, allowing the mismatch to be removed and the correct nucleotide to be reinserted.
The collaboration of the exonuclease activity of DNA polymerase and the post-replicative mismatch repair system ensures that DNA replication is incredibly accurate. These processes allow cells to maintain the fidelity of genetic information, which is essential for the proper functioning and survival of organisms.
