InterPro domain: IPR034922

Proteins containing this domain are composed of RNA exonuclease 1 (REX1 or Rex1p), REX3 (or Rex3p), and similar eukaryotic proteins. In yeast, REX1 and REX3 are required for 5S rRNA and MRP (mitochondrial RNA processing) RNA maturation, respectively [ 1 ]. 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 [ 2 ].

REX1 is the major exonuclease from this family responsible for pre-tRNA trail trimming and may also be involved in nuclear CCA turnover [ 3 ]. REX proteins function in the processing and maturation of many RNA species, similar to the function of Escherichia coli RNase T [ 4 ].

1. Three conserved members of the RNase D family have unique and overlapping functions in the processing of 5S, 5.8S, U4, U5, RNase MRP and RNase P RNAs in yeast. EMBO J. 19, 1357-65
2. Exoribonuclease superfamilies: structural analysis and phylogenetic distribution. Nucleic Acids Res. 29, 1017-26
3. Competition between the Rex1 exonuclease and the La protein affects both Trf4p-mediated RNA quality control and pre-tRNA maturation. RNA 14, 1214-27