Given the essential nature of PRPP, all free-living organisms contain at least one gene
encoding PRPP synthetase . Recently four PRS cDNAs were isolated from Arabidopsis by functional complementation of an Escherichia coli mutant lacking PRS activity .
A fifth PRS sequence that predicts a protein with high amino acid
sequence homology to the other Arabidopsis PRSs, particularly with PRS1 and 2 was located on chromosome II and designated PRS5 . Kinetic characterization of the gene products of PRS1-4 indicated that PRS3 and 4 represent a novel class of PRSs since their
activities are independent of inorganic phosphate.