This is a large group of enzymes which, together with those now listed as EC
3.1.21.3 (type I site-specific deoxyribonuclease) and EC
3.1.21.4 (type II site-specific deoxyribonuclease), were previously listed separately in sub-subclasses EC 3.1.23 and EC 3.1.24. They have an absolute requirement for ATP but do not hydrolyse it; S-adenosy-L-methionine stimulates the reaction, but is not absolutely required. They recognize specific, short DNA sequences and cleave a short distance away from the recognition sequence. These enzymes exist as complexes with enzymes of similar specificity listed under EC
2.1.1.72 [site-specific DNA-methyltransferase (adenine-specific)] or EC
2.1.1.37 [DNA (cytosine-5-)-methyltransferase].
