Type I site-specific deoxyribonuclease (, type I restriction enzyme, deoxyribonuclease (ATP- and S-adenosyl-L-methionine-dependent), restriction-modification system, deoxyribonuclease (adenosine triphosphate-hydrolyzing), adenosine triphosphate-dependent deoxyribonuclease, ATP-dependent DNase, type 1 site-specific deoxyribonuclease) is an enzyme. This enzyme catalyses the following chemical reaction
They have an absolute requirement for ATP (or dATP) and S-adenosyl-L-methionine.