This is a highly divergent 3' exoribonuclease family. The proteins constitute a typical RNase fold, where the active site residues form a magnesium catalytic centre. The protein of the solved structure readily cleaves 3' overhangs in a time-dependent manner. It is similar to DEDD-type RNases and is an unusual ATP-binding protein that binds ATP and dATP. It forms a dimer in solution and both protomers in the asymmetric unit bind a magnesium ion through Asp-6 in SwissProt:P9WJ73 [1]. Proteins containing this domain also include 3'-5' exonuclease dexA from bacteriophage T4. It may play a role in the final step of host DNA degradation, by scavenging DNA into mononucleotides [2,3].

1: Mycobacterium tuberculosis Rv2179c protein establishes a new exoribonuclease family with broad phylogenetic distribution. Abendroth J, Ollodart A, Andrews ES, Myler PJ, Staker BL, Edwards TE, Arcus VL, Grundner C; J Biol Chem. 2014;289:2139-2147. PMID:24311791

2: Role of exonucleolytic degradation in group I intron homing in phage T4. Huang YJ, Parker MM, Belfort M; Genetics. 1999;153:1501-1512. PMID:10581261

3: Effect of DNA sequence and structure on nuclease activity of the DexA protein of bacteriophage T4. Gruber H, Kern G, Gauss P, Gold L; J Bacteriol. 1988;170:5830-5836. PMID:3056918