DEDDh 3'-5' exonuclease domain of oligoribonuclease and similar proteins
Oligoribonuclease (Orn) is a DEDDh-type DnaQ-like 3'-5' exoribonuclease that is responsible for degrading small oligoribonucleotides to mononucleotides. It contains 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. Orn is essential for Escherichia coli survival. The human homolog, also called Sfn (small fragment nuclease), is able to hydrolyze short single-stranded RNA and DNA oligomers. It plays a role in cellular nucleotide recycling.