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 Endonucleolytic cleavage of DNA to give random double-stranded fragments with terminal 5'-phosphates; ATP is simultaneously hydrolysed They have an absolute requirement for ATP (or dATP) and S-adenosyl-L-methionine. See also Restriction enzyme References External links EC 3.1.21