The restriction (R) subunit of a type I restriction enzyme that recognizes 5'-GAAN(7)RTCG-3' and cleaves a random distance away. Subunit R is required for both nuclease and ATPase activities, but not for modification (Probable) (PubMed:12654995). After locating an unmethylated recognition site, the enzyme complex serves as a molecular motor that translocates DNA in an ATP-dependent manner until a collision occurs that triggers cleavage (Probable). The enzyme undergoes major structural changes to bring the motor domains into contact with DNA, allowing DNA translocation. This prevents DNA access to the catalytic domains of both the R and M subunits, preventing both restriction and methylation (PubMed:32483229). Endonucleolytic cleavage of DNA to give random double-stranded fragments with terminal 5'-phosphates, ATP is simultaneously hydrolyzed. The type I restriction/modification system is composed of three polypeptides R, M and S; the restriction enzyme has stoichiometry R(2)M(2)S(1) while the methyltransferase is M(2)S(1). There is an equilibrium between R(2)M(2)S(1) and R(1)M(2)S(1); the latter is methylation and translocation proficient but restriction deficient. (Microbial infection) Holoenenzyme interacts with Escherichia phage T7 protein Ocr; this interaction leads to the inhibition of the restriction activity, but may still allow methylation and translocation. The individual domains assume different positions in the enzyme, allowing the holoenzyme to regulate the methylase, endonuclease and translocation states. Deletion of the linkers between the domains prevents movelemt and thus restriction activity. Type I restriction and modification enzymes are complex, multifunctional systems which require ATP, S-adenosyl methionine and magnesium as cofactors and, in addition to their endonucleolytic and methylase activities, are potent DNA-dependent ATPases. Belongs to the HsdR family.