Arabidopsis thaliana gene At5g06450 encodes a putative DnaQ-like 3′-5′ exonuclease domain-containing protein (AtDECP). The DnaQ-like 3′-5′ exonuclease domain is often found as a proofreading domain of DNA polymerases. The overall structure of AtDECP adopts an RNase H fold that consists of a mixed β-sheet flanked by α-helices. Interestingly, AtDECP forms a homohexameric assembly with a central six fold symmetry, generating a central cavity. The ring-shaped structure and comparison with WRN-exo, the best structural homologue of AtDECP, suggest a possible mechanism for implementing its exonuclease activity using positively charged patch on the N-terminal side of the homohexameric assembly. The homohexameric structure of AtDECP provides unique information about the interaction between the DnaQ-like 3′-5′ exonuclease and its substrate nucleic acids.Proteins 2013. © 2013 Wiley Periodicals, Inc.