Restriction-modification (R-M) systems protect a bacterial cell against invasion of foreign DNA by endonucleolytic cleavage of DNA that lacks a site specific modification. The R-M system is a complex containing three polypeptides: M (this family), S (Pfam:PF01420), and R [1]. This family consists of N-6 adenine-specific DNA methylase EC:2.1.1.72 from Type I and Type IC restriction systems. These methylases have the same sequence specificity as their corresponding restriction enzymes.

1: A type IC restriction-modification system in Lactococcus lactis. Schouler C, Clier F, Lerayer AL, Ehrlich SD, Chopin MC; J Bacteriol 1998;180:407-411. PMID:9440532

2: Combinational variation of restriction modification specificities in Lactococcus lactis. Schouler C, Gautier M, Ehrlich SD, Chopin MC; Mol Microbiol 1998;28:169-178. PMID:9593305

3: The specificity of sty SKI, a type I restriction enzyme, implies a structure with rotational symmetry. Thorpe PH, Ternent D, Murray NE; Nucleic Acids Res 1997;25:1694-1700. PMID:9108149