prsB is an allele of the Salmonella typhimurium prsA gene: characterization of a mutant phosphoribosylpyrophosphate synthetase.
The Salmonella typhimurium prsB mutation was previously mapped at 45 min on the chromosome, and a prsB strain was reported to produce undetectable levels of phosphoribosylpyrophosphate (PRPP) synthetase activity and very low levels of immunologically cross-reactive protein in vitro (N.K. Pandey and R.L. Switzer, J. Gen. Microbiol, 128:1863-1871, 1982). We have shown by P22-mediated transduction that the prsB gene is actually an allele of prsA, the structural gene for PRPP synthetase, which maps at 35 min. The prsB (renamed prs-100) mutant produces about 20% of the activity and 100% of the cross-reactive material of wild-type strains. prs-100 mutant strains are temperature sensitive, as is the mutant PRPP synthetase in vitro. The prs-100 mutation is a C-to-T transition which results in replacement of Arg-78 in the mature wild-type enzyme by Cys. The mutant PRPP synthetase was purified to greater than 98% purity. It possessed elevated Michaelis constants for both ATP and ribose-5-phosphate, a reduced maximal velocity, and reduced sensitivity to the allosteric inhibitor ADP. The mutant enzyme had altered physical properties and was susceptible to specific cleavage at the Arg-101-to-Ser-102 bond in vivo. It appears that the mutation alters the enzyme's kinetic properties through substantial structural alterations rather than by specific perturbation of substrate binding or catalysis.
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Department of Biochemistry, University of Illinois, Urbana 61801.
Switzer
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RL
D000483:Alleles; D002413:Cations, Divalent; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D006358:Hot Temperature; D007700:Kinetics; D008970:Molecular Weight; D009154:Mutation; D010641:Phenotype; D015183:Restriction Mapping; D012268:Ribose-Phosphate Pyrophosphokinase / Q000037:antagonists & inhibitors / Q000235:genetics*; D012486:Salmonella typhimurium / Q000235:genetics*
D002413:Cations, Divalent; D012268:Ribose-Phosphate Pyrophosphokinase