This is a large group of enzymes which, together with those now listed as EC
3.1.21.4 (type II site-specific deoxyribonuclease) and EC
3.1.21.5 (type III 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 (or dATP) and S-adenosyl-L-methionine. They recognize specific short DNA sequences and cleave at sites remote from the recognition sequence. They are multifunctional proteins that also catalyse the reactions of EC
2.1.1.72 [site-specific DNA-methyltransferase (adenine-specific)] and EC
2.1.1.37