f The defective phosphoribosyl diphosphate synthase in a temperature-sensitive prs-2 mutant of Escherichia coli is compensated by increased enzyme synthesis
- Authors: David A. Post†, Robert L. Switzer, Bjarne Hove-Jensen
- Author for correspondence: Bjarne Hove-Jensen. Tel: +45 3532 2027. Fax: +45 3532 2040. e-mail: email@example.com
- Microbiology, February 1996 142: 359-365, doi: 10.1099/13500872-142-2-359
- Subject: Genetics And Molecular Biology
- Published Online:
Summary: An Escherichia coli strain which is temperature-sensitive for growth due to a mutation(prs-2)causing a defective phosphoribosyl diphosphate(PRPP)synthase has been characterized. The temperature-sensitive mutation was mapped to a 276 bp HindIII-BssHII DNA fragment located within the open reading frame specifying the PRPP synthase polypeptide. Cloning and sequencing of the mutant allele revealed two mutations. One, a G→A transition, located in the ninth codon, was responsible for the temperature-conditional phenotype and resulted in a serine residue at this position. The wild-type codon at this position specified a glycine residue that is conserved among PRPP synthases across a broad phylogenetic range. Cells harbouring the glycine-to-serine alteration specified by a plasmid contained approximately 50% of the PRPP synthase activity of cells harbouring a plasmid-borne wildtype allele, both grown at 25°C. The mutant enzyme had nearly normal heat stability, as long as it was synthesized at 25°C. In contrast, there was hardly any PRPP synthase activity or anti-PRPP synthase antibody cross-reactive material present in cells harbouring the glycine to serine alteration following temperature shift to 42°C. The other mutation was aC→T transition located 39 bp upstream of the G→A mutation, i.e. outside the coding sequence and close to the Shine-Dalgarno sequence. Cells harbouring only the C→T mutation in a plasmid contained approximately three times as much PRPP synthase activity as a strain harbouring a plasmid-borne wild-type prs allele. In cells harbouring both mutations, the C→T mutation appeared to compensate for the G→A mutation by increasing the amount of a partially defective enzyme at the permissive temperature.
Present address: Abbott Laboratories, Strain Development Department, 1401 Sheridan Road, North Chicago, IL 60064, USA.
- Keyword(s): phosphoribosylpyrophosphate, nucleotide synthesis, RNA analysis, PRPP synthase, prs gene
© Society for General Microbiology 1996 | Published by the Microbiology Society
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