A type III restriction enzyme that recognizes 2 inversely oriented double-stranded sequences 5'-CAGCAG-3' and cleaves DNA 25-27 base pairs downstream of one site. DNA restriction requires both the Res and Mod subunits (PubMed:11178902, PubMed:15464603). DNA topology affects its action; relaxed and negatively supercoiled DNA are digested but positively supercoiled DNA is not a good substrate (PubMed:11178902). Interacts with DNA approximately one half-turn downstream of the recognition site (PubMed:26067164). After binding to one recognition site undergoes random one-dimensional diffusion along DNA until it collides with a stationary enzyme bound to the second DNA site, which is when DNA cleavage occurs (Probable). Endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. A heterotetramer with stoichiometry Res(2)Mod(2) (PubMed:11178902). A heterotrimer with stoichiometry Res(1)Mod(2) (PubMed:26067164). Has a helicase-type domain in its N-terminus and an endonuclease-type domain in its C-terminus. AMP lies in a cleft in the helicase domain. Belongs to the type III restriction-modification system Res protein family.