The restriction endonuclease from E. coli B is both an endonuclease and a DNA methylase. Both activities either require or are stimulated by Mg(+2), adenosine triphosphate, and S-adenosyl-L-methionine. The particular activity which the enzyme exhibits depends upon the nature of the SB sites, the genetic sites that identify substrate DNA. Enzymatic treatment of DNA that has an unmodified, wild-t...
