the central domain of a trifunctional enzyme that contains a PRAI C-terminal domain and a glutamine amidotransferase ( EC 2.4.2.- ) (GATase) N-terminal domain. A structure of the IGPS domain of the bifunctional enzyme from the mesophilic bacterium E. coli (eIGPS) has been compared with the monomeric indole-3-glycerol phosphate synthase from