Type I restriction enzyme R protein N-terminus (HSDR_N)
This family consists of a number of N terminal regions found in type I restriction enzyme R (HSDR) proteins. Restriction and modification (R/M) systems are found in a wide variety of prokaryotes and are thought to protect the host bacterium from the uptake of foreign DNA. Type I restriction and modification systems are encoded by three genes: hsdR, hsdM, and hsdS. The three polypeptides, HsdR, HsdM, and HsdS, often assemble to give an enzyme (R2M2S1) that modifies hemimethylated DNA and restricts unmethylated DNA.