Structure of the gene encoding phosphoribosylpyrophosphate synthetase (prsA) in Salmonella typhimurium

The Salmonella typhimurium gene prsA, which encodes phosphoribosylpyrophosphate synthetase, has been cloned, and the nucleotide sequence has been determined. The amino acid sequence derived from the S. typhimurium gene is 99% identical to the derived Escherichia coli sequence and 47% identical to two rat isozyme sequences. Strains containing plasmid-borne prsA have been used to overproduce and purify the enzyme. The promoter for the S. typhimurium prsA gene was identified by deletion analysis and by similarity to the promoter for the E. coli prsA gene. The location of the prsA promoter results in a 416-base-pair 5' untranslated leader in the prsA transcript, which was shown by deletion to be necessary for maximal synthesis of phosphoribosylpyrophosphate synthetase. The S. typhimurium leader contains a 115-base-pair insert relative to the E. coli leader. The insert appears to have no functional significance.