The protein encoded by this gene is a member of the purine/pyrimidine phosphoribosyltransferase family. It is a regulatory allosteric enzyme that catalyzes the first step of de novo purine nucleotide biosythetic pathway. This gene and PAICS/AIRC gene, a bifunctional enzyme catalyzing steps six and seven of this pathway, are located in close proximity on chromosome 4, and divergently transcribed from an intergenic region. [provided by RefSeq, Mar 2011].