This domain is found at the N-terminus of the Mrr restriction endonuclease catalytic domain, Pfam:PF04471 [1,2]. Fold recognition analysis predicts that it is a diverged member of the winged helix variant of helix turn helix proteins. It may play a role in DNA sequence recognition [2].

1: 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

2: Mutational analysis and a structural model of methyl-directed restriction enzyme Mrr. Orlowski J, Mebrhatu MT, Michiels CW, Bujnicki JM, Aertsen A; Biochem Biophys Res Commun. 2008;377:862-866. PMID:18951880