AIR (aminoimidazole ribonucleotide) synthase related protein. This family includes Hydrogen expression/formation protein HypE, AIR synthases, FGAM (formylglycinamidine ribonucleotide) synthase and Selenophosphate synthetase (SelD). The N-terminal domain of AIR synthase forms the dimer interface of the protein, and is suggested as a putative ATP binding domain.