DNA polymerase 3′–5′ exonuclease domain (3'-5' Exo)

The DNA polymerase 3′–5′ exonuclease domain is a specialized catalytic region within high-fidelity DNA polymerases, primarily DNA polymerase epsilon (POLE) and delta (POLD1), which are responsible for leading and lagging strand synthesis. This domain performs a critical proofreading function by identifying and excising incorrectly incorporated nucleotides at the 3' end of the nascent DNA strand, thereby reducing the replication error rate by several orders of magnitude (UniProt Q07864). In clinical oncology, germline or somatic mutations within this domain lead to a proofreading deficiency, resulting in an ultramutated phenotype characterized by a massive accumulation of single nucleotide variants (Nature Reviews Cancer, PMID: 27658528). These mutations are strongly associated with Polymerase Proofreading-Associated Polyposis (PPAP) and various sporadic cancers, most notably colorectal and endometrial carcinomas (PubMed, PMID: 23447401). While the site is not typically a target for direct pharmacological inhibition, it is a critical determinant of the efficacy of nucleoside analog drugs, which must either resist or overwhelm exonuclease activity to cause chain termination (PubChem). Furthermore, the presence of mutations in this domain serves as a potent biomarker for treatment with immune checkpoint inhibitors, as the high neoantigen load in these tumors enhances the anti-tumor immune response (NEJM, PMID: 26028255).

Other names

Proofreading domain3'-5' exonuclease active sitePOLE exonuclease domainPOLD1 exonuclease domainExonuclease domain of DNA polymerase epsilonExonuclease domain of DNA polymerase delta

Excision of mismatched nucleotides to maintain replication fidelity; evasion of excision by therapeutic nucleoside analogs; induction of neoantigens in proofreading-deficient tumors.