The phosphoribosylaminoimidazolesuccinocarboxamide synthase activity of cytosolic PAICS (multifunctional protein ADE2) catalyzes the reaction of 5'-phosphoribosyl-5-aminoimidazole-4-carboxylate (CAIR), L-aspartate, and ATP to form 5'-phosphoribosyl-5-aminoimidazole-4-N-succinocarboxamide (SAICAR), ADP, and orthophosphate. Chicken PAICS protein has been purified and its catalytic properties analyzed in vitro (Firestine and Davisson 1994). The native chicken protein behaves as a large multimer on gel filtration; it is inferred to be a octamer by analogy to the human protein (Li et al. 2007). The subcellular location of the chicken enzyme is inferred from that of its better-characterized mammalian counterparts.