This family of proteins is found in bacteria, archaea and eukaryotes. Proteins in this family are typically between 201 and 230 amino acids in length. There is a single completely conserved residue E that may be functionally important. This family is distantly similar to Pfam:PF01885. Studies in search for novel ADP-ribosylation systems in bacterial genomes have identified an operon that encodes a conserved protein containing a distinct type of macrodomain associated with this family. This led to the identification of a toxin-antitoxin (TA) system, with DarT acting as the toxin. It is an enzyme that specifically modifies thymidines on single-stranded DNA in a sequence-specific manner by a nucleotide-type modification called ADP-ribosylation. This modification in turn can be removed by DarG, the antitoxin macrodomain protein. In addition, it was illustrated that substitution of the single completely conserved glutamate residue resulted in attenuation of function where DarT was non-toxic [1].

1: The Toxin-Antitoxin System DarTG Catalyzes Reversible ADP-Ribosylation of DNA. Jankevicius G, Ariza A, Ahel M, Ahel I; Mol Cell. 2016;64:1109-1116. PMID:27939941