The phosphoribosylglycinamide formyltransferase activity of cytosolic GART trifunctional enzyme (trifunctional purine biosynthetic protein adenosine-3) catalyzes the reaction of 5-phosphoribosylglycinamide (GAR) and 10-formyl-tetrahydrofolate to form 5'-phosphoribosylformylglycinamide (FGAR) and tetrahydrofolate. GART trifunctional protein has been purified from chicken liver (Daubner et al. 1985), and a cDNA encoding the chicken enzyme has been identified based on sequence similarities and its ability to complement E. coli cells whose homologous purine biosynthesis genes were mutated (Aimi et al. 1990). The subcellular location of the chicken enzyme is inferred from that of its better-characterized mammalian counterparts.