DEDDy 3'-5' exonuclease domain of RNase D, WRN, and similar proteins
The RNase D-like group is composed of RNase D, WRN, and similar proteins. They contain a DEDDy-type, DnaQ-like, 3'-5' exonuclease domain that contains three conserved sequence motifs termed ExoI, ExoII and ExoIII, with a specific YX(3)D 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. RNase D is involved in the 3'-end processing of tRNA precursors. RNase D-like proteins in eukaryotes include yeast Rrp6p, human PM/Scl-100 and Drosophila melanogaster egalitarian (Egl) protein. WRN is a unique DNA helicase possessing exonuclease activity. Mutation in the WRN gene is implicated in Werner syndrome, a disease associated with premature aging and increased predisposition to cancer. Yeast Rrp6p and the human Polymyositis/scleroderma autoantigen 100kDa (PM/Scl-100) are exosome-associated proteins involved in the degradation and processing of precursors to stable RNAs. Egl is a component of an mRNA-binding complex which is required for oocyte specification. The Egl subfamily does not possess a completely conserved YX(3)D pattern at the ExoIII motif.