This family represents the C-terminus of bacterial enzymes similar to type II restriction endonucleases BsuBI and PstI (EC:3.1.21.4). The enzymes of the BsuBI restriction/modification (R/M) system recognise the target sequence 5'CTGCAG and are functionally identical with those of the PstI R/M system [1].

1: BsuBI--an isospecific restriction and modification system of PstI: characterization of the BsuBI genes and enzymes. Xu GL, Kapfer W, Walter J, Trautner TA; Nucleic Acids Res 1992;20:6517-6523. PMID:1480472

2: Sequence, structure and functional diversity of PD-(D/E)XK phosphodiesterase superfamily. Steczkiewicz K, Muszewska A, Knizewski L, Rychlewski L, Ginalski K; Nucleic Acids Res. 2012;40:7016-7045. PMID:22638584