DEDDh 3'-5' exonuclease domain of the eukaryotic exoribonucleases PAN2, RNA exonuclease (REX)-1,-3, and -4, ISG20, and similar proteinsThis group is composed of eukaryotic exoribonucleases that include PAN2, RNA exonuclease 1 (REX1 or Rex1p), REX3 (Rex3p), REX4 (or Rex4p), ISG20, and similar proteins. They are DEDDh-type DnaQ-like 3'-5' exonucleases containing three conserved sequence motifs termed ExoI, ExoII and ExoIII, with a specific Hx(4)D conserved pattern at ExoIII. These motifs are clustered around the active site and contain four conserved acidic residues that serve as ligands for the two metal ions required for catalysis. PAN2 is the catalytic subunit of poly(A) nuclease (PAN), a Pab1p-dependent 3'-5' exoribonuclease which plays an important role in the posttranscriptional maturation of pre-mRNAs. REX proteins are required for the processing and maturation of many RNA species, and ISG20 is an interferon-induced antiviral exonuclease with a strong preference for single-stranded RNA.