This family includes the HpaII (recognises and cleaves C^CGG) restriction endonuclease.

1: DNA looping by two-site restriction endonucleases: heterogeneous probability distributions for loop size and unbinding force. Gemmen GJ, Millin R, Smith DE; Nucleic Acids Res. 2006;34:2864-2877. PMID:16723432

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