Phosphoribosylpyrophosphate synthetase of Escherichia coli. Properties of the purified enzyme and primary structure of the prs gene.

Abstract

Phosphoribosylpyrophosphate (P-Rib-PP) synthetase of Escherichia coli has been purified to near homogeneity from a strain harboring the prs gene, encoding P-Rib-PP synthetase, on a multicopy plasmid. Analysis of the enzyme showed that it required inorganic phosphate for activity and for stability. Magnesium ions were required both as a complex with the substrate ATP and as a free cation. P-Rib-PP synthetase activity was inhibited strongly by ADP. Kinetic analysis indicated multiple sites of action of ADP. In addition apparent substrate inhibition was exerted by ribose 5-phosphate in the presence of ADP. The nucleotide sequence of the E. coli prs gene has been determined and the coding segment established. The deduced amino acid sequence of P-Rib-PP synthetase contained 314 amino acid residues and the molecular weight was calculated as 34,060. The initiation site of transcription was determined. This site was preceded by well conserved -10 and -35 consensus sequences (pdT-dA-dG-dA-dA-dT and pdT-dT-dG-dA-dT-dG, respectively). The transcription initiation site preceded the potential translation initiation site by 302 nucleotides. Transcription terminated approximately 35 nucleotides downstream from the UAA translation stop codon, within a Thy-rich region following an inverted repeat sequence, indicative of an rho-independent transcription terminator.