EcoEI R protein C-terminal protein (IPR013670) is involved. We classify restriction endonucleases into four categories: type I, type II, type III, and type IV. Different kinds of enzymes can recognize certain short DNA sequences and cut DNA at the ends to make specific double-stranded pieces with 5'-phosphates at the ends. Type I enzymes are multifunctional proteins that possess methylase and restriction activities. They cleave at sites that are distant from the recognition site and require ATP and S-adenosyl-L-methionine to function. Type III enzymes cleave at a site that is not far from the recognition site, require ATP (but do not hydrolyze), and exist as complexes with the modification methylase methylase. S-adenosyl-L-methionine stimulates the reaction, but it is not essential. This entry denotes the C-terminal domain that is present in the R subunit of the type I enzyme and the Res subunit of the type III enzyme. You need the R protein (HsdR) to do both nuclease and ATPase activities, and Type I enzymes like EcoEI can recognize 5'-GAGN(7)ATGC-3.