This family includes the CfrBI (recognises and cleaves C^CWWGG) restriction endonuclease.

1: Cloning and sequences of the genes encoding the CfrBI restriction-modification system from Citrobacter freundii. Zakharova MV, Kravetz AN, Beletzkaja IV, Repyk AV, Solonin AS; Gene. 1993;129:77-81. PMID:8335262

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