5-[(5-phospho-1-deoxy-D-ribulos-1-ylimino)methylamino]-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide + NH4(+) = D-erythro-1-(imidazol-4-yl)glycerol 3-phosphate + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide + H2O + H(+) — reaction