This enzyme has been characterised and shown to belong to a new family of the type I class of restriction and modification enzymes. This family is involved in bacterial defence by making double strand breaks in specific double stranded DNA sequences, e.g. that of invading bacteriophages. EcoR124 is made up of three subunits, HsdR, HsdS and HsdM. The R subunit has ATPase and restriction endonuclease activity. This domain is the C terminal of the R subunit [1].

1: Basis for changes in DNA recognition by the EcoR124 and EcoR124/3 type I DNA restriction and modification enzymes. Price C, Lingner J, Bickle TA, Firman K, Glover SW; J Mol Biol. 1989;205:115-125. PMID:2784505