The subtype B restriction (R) subunit of a type I restriction enzyme that recognizes 5'-GAGN(7)GTCA-3' and cleaves a random distance away. Subunit R is required for both nuclease and ATPase activities, but not for modification. After locating a non-methylated 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. 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 (PubMed:6325176). The restriction enzyme has stoichiometry R(2)M(2)S(1) while the methyltransferase is M(2)S(1) (By similarity). 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.