This domain is about 100 amino acid residues in length. It is found in the MazG protein from E. coli. It contains four conserved negatively charged residues that probably form an active site or metal binding site. This domain is found in isolation in some proteins as well as associated with pfam00590. This domain is clearly related to pfam01503 another pyrophosphohydrolase involved in histidine biosynthesis. This family may be structurally related to the NUDIX domain pfam00293 (Bateman A pers. obs.).