ATP Hydrolysis by Restriction Endonuclease from E. coli K

We wish to report a puzzling ATPase activity associated with the DNA restriction endonuclease from E. coli strain K^1–3. This enzyme makes a limited number of double chain breaks in DNA molecules lacking the host-controlled modification imparted by strain K. Unmodified DNA molecules from bacteriophage λ, which serve as a convenient substrate, are broken into fragments with a weight average molecular weight of approximately 7 × 10⁶, about one-fifth the size of the intact λ chromosome. The reaction requires Mg2⁺, ATP and S-adenosylmethionine (SAM).