Members of this group are distantly related to MazG-type NTP pyrophosphohydrolase . Conserved residues of the MazG domain (at least three of the Glu residues, Asp, Lys and Arg), including those shown to be functionally important, are also conserved here. MazG protein of Thermotoga maritima has been shown to have both nucleoside triphosphate pyrophosphohydrolase and pyrophosphatase activities, while Escherichia coli MazG has only NTP pyrophosphohydrolase activity. Therefore, members of this group are tentatively predicted to be pyrophosphohydrolases.