HUMAN X-LINKED PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE SUPERACTIVITY IS ASSOCIATED WITH DISTINCT POINT MUTATIONS IN THE PRPS1 GENE

Superactivity of phosphoribosylpyrophosphate synthetase (PRS) is an X chromosome-linked disorder of purine metabolism, characterized by gout with uric acid overproduction and, in some families, neurodevelopment al impairment. Two highly homologous isoforms of PRS (PRS1 and PRS2), each encoded by a distinct X chromosome-linked locus, have been identi fied, and PRS1 and 2 cDNAs have been cloned. The entire 954-base pair translated regions of PRS1 and 2 cDNAs derived from cultured lymphobla sts and fibroblasts from two patients in whom purine nucleotide feedba ck resistance of PRS is associated with enzyme superactivity and neuro developmental defects were examined by direct sequencing after polymer ase chain reaction amplification of PRS transcripts. Nucleotide sequen ces of PRS2 cDNAs from the patients and normal individuals were identi cal. In contrast, PRS1 cDNAs from the patients differ from normal PRS1 cDNA, each by a single base substitution. PRS1 cDNA from patient N. B . showed an A to G transition at nucleotide 341, corresponding to an a sparagine to serine change at amino acid residue 113 of mature PRS1. A G to C transversion at nucleotide 547, indicating an aspartic acid to histidine change at amino acid 182, was found for PRS1 cDNA from pati ent S. M. Point mutations at the sites identified in the PRS1 cDNAs of the two patients were confirmed by the results of RNase mapping analy sis. Normal, N. B., and S. M. PRS1 cDNAs were introduced into Escheric hia coli BL21(DE3)/pLysS, and recombinant N. B. and S. M. PRS1s showed the purine nucleotide feedback resistance phenotypes characteristic o f PRS from patients' cells.