The EcoDXX 1 restriction and modification system of Escherichia coli ET 7. Purification, subunit structure and properties of the restriction endonuclease

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Abstract
The Escherichia coli plasmid pDXX1 codes for a new restriction-modification system. The specific restriction endonuclease coded by this system has been purified by a procedure that includes phosphocellulose and heparin-agarose chromatography. Sedimentation on glycerol gradients showed one peak of activity with a value of about 12 S. The highly purified enzyme require ATP and Mg2+ for activity as well as S-adenosylmethionine, although some S-adenosylmethionine molecules are probably bound to the enzyme. The enzyme does not cleave .lambda. DNA at well-defined sites and has a strong non-modified DNA-dependent ATPase activity. The enzyme has also methylase activity acting against non-modified DNA.