Mutant Strains of Salmonella typhimurium with Defective Phosphoribosylpyrophosphate Synthetase Activity

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Abstract
A mutant of S. typhimurium with undetectable phosphoribosylpyrophosphate (PRPP) synthetase (EC 2.7.6.1) activity in vitro and abnormally low PRPP pools in vivo was identified by screening temperature-sensitive isolates by an autoradiographic procedure. The lack of PRPP synthetase activity in vitro and temperature-sensitive growth resulted from separate, but closely linked mutations mapping at 47 units on the Salmonella chromosome. Mutant cell extracts prepared by a variety of methods did not show any detectable PRPP synthetase activity, but material that was immunochemically cross-reactive with PRPP synthetase was detected by complement fixation analysis. A 2nd mutant, isolated by localized mutagenesis, contained about half the PRPP synthetase and cross-reacting material of the parental strain.