The link between restriction endonuclease fidelity and oligomeric state: A study with Bse634I

► Type II restriction endonucleases (REases) exist as monomers, dimers and tetramers. ► Fidelity of tetrameric and dimeric forms of the Bse634I REase was analysed in vitro. ► Tetramerisation did not increase Bse634I fidelity compared to the dimeric variant. ► Tetramerisation of Bse634I provided a safety-catch to prevent host DNA cleavage.