This family of proteins is found in archaea and viruses. Proteins in this family are typically between 211 and 244 amino acids in length. These proteins are nucleases from fusseloviruses and sulfolobus archaea.

1: 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