Prokaryotic family found in type II restriction enzymes containing the hallmark (D/E)-(D/E)XK active site. Presence of catalytic residues implicates this region in the enzymatic cleavage of DNA [1,2].

1: Characterization and expression of the Escherichia coli Mrr restriction system. Waite-Rees PA, Keating CJ, Moran LS, Slatko BE, Hornstra LJ, Benner JS; J Bacteriol 1991;173:5207-5219. PMID:1650347

2: Identification of a PD-(D/E)XK-like domain with a novel configuration of the endonuclease active site in the methyl-directed restriction enzyme Mrr and its homologs. Bujnicki JM, Rychlewski L; Gene 2001;267:183-191. PMID:11313145