Nucleoside triphosphate pyrophosphatase that hydrolyzes 7-methyl-GTP (m(7)GTP). May have a dual role in cell division arrest and in preventing the incorporation of modified nucleotides into cellular nucleic acids. H2O + N(7)-methyl-GTP = diphosphate + H(+) + N(7)-methyl-GMP Belongs to the Maf family. YceF subfamily.