# EXO1

Source: https://onco.cc/targets/exo1/  
OnCo record `exo1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

EXO1 (Exonuclease 1) is an enzyme. The public catalogues list it as a DNA repair gene, and the evidence so far is association rather than a proven role. Tied to Breast cancer.

## Summary

5'->3' double-stranded DNA exonuclease which may also possess a cryptic 3'->5' double-stranded DNA exonuclease activity. Functions in DNA mismatch repair (MMR) to excise mismatch-containing DNA tracts directed by strand breaks located either 5' or 3' to the mismatch. Also exhibits endonuclease activity against 5'-overhanging flap structures similar to those generated by displacement synthesis when DNA polymerase encounters the 5'-end of a downstream Okazaki fragment.

Open Targets scores its association with cancer at 0.68 (direct and indirect evidence; datatypes literature 0.98, affected pathway 0.87, genetic association 0.74, genetic literature 0.01).

## Fields

- Kind: Target
- Last checked: 2026-09-23
- Also known as: exonuclease 1; Exonuclease 1; HEX1; hExoI
- Tags: cancer-genes-wave
- Symbol: EXO1
- Class: enzyme
- Biology: 5'->3' double-stranded DNA exonuclease which may also possess a cryptic 3'->5' double-stranded DNA exonuclease activity. Functions in DNA mismatch repair (MMR) to excise mismatch-containing DNA tracts directed by strand breaks located either 5' or 3' to the mismatch. Also exhibits endonuclease activity against 5'-overhanging flap structures similar to those generated by displacement synthesis when DNA polymerase encounters the 5'-end of a downstream Okazaki fragment. Required for somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin genes. Essential for male and female meiosis. Location: Nucleus (UniProt). Locus 1q43 (HGNC).
- Where found: Breast cancer: Open Targets association 0.54 with breast cancer (MONDO_0007254)

## Notes

- Written by scripts/fetch-cancer-genes.ts from CIViC, Open Targets, IntOGen, HGNC and UniProt; the function text is UniProt's, condensed and in UK spelling. Roles: UniProt keyword "DNA repair". Evidence tier "association-only" is the strongest of those signals.
- Prevalence not recorded: none of the sources gives a positivity rate.

## Sources

- HGNC HGNC:3511: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:3511
- UniProt Q9UQ84: https://www.uniprot.org/uniprotkb/Q9UQ84/entry
- NCBI Gene 9156: https://www.ncbi.nlm.nih.gov/gene/9156
- Ensembl ENSG00000174371: https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000174371

## Connected records

- collections: [Open Targets Platform](https://onco.cc/collections/open-targets/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/)
- pathways: [Mismatch repair & microsatellite instability](https://onco.cc/pathways/mismatch-repair-msi/)

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JSON: https://onco.cc/api/v1/entities/exo1.json