3' to 5' exonuclease activity improves the fidelity of polymerase activity

 The 3' to 5' exonuclease activity of polymerases extremely improves the fidelity of enzyme that results in synthesis of products having few errors. When a polymerase protein possesses an exonuclease activity in its conformation, a misincorporated nucleotide is recognized after forming of phosphodiester bond with the 3'OH of primer by the nuclease domain, and thereafter such misincorporated nucleotide is removed by the nuclease activity. Therefore, high fidelity polymerases that are commercially available used for PCR-related assays often possess the 3' to 5' exonuclease activity.