DEDDh 3'-5' exonuclease domain of Caenorhabditis elegans ERI-1, human 3' exonuclease, and similar proteins
This subfamily is composed of Caenorhabditis elegans ERI-1, human 3' exonuclease (3'hExo), Drosophila exonuclease snipper (snp), and similar proteins from eukaryotes and bacteria. These 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. ERI-1 has been implicated in the degradation of small interfering RNAs (RNAi). 3'hExo participates in the degradation of histone mRNAs. Snp is a non-essential exonuclease that efficiently degrades structured RNA and DNA substrates as long as there is a minimum of 2 nucleotides in the 3' overhang to initiate degradation. Snp is not a functional homolog of either ERI-1 or 3'hExo.