%0 Journal Article %A Post, David A. %A Switzer, Robert L. %A Hove-Jensen, Bjarne %T The defective phosphoribosyl diphosphate synthase in a temperature-sensitive prs-2 mutant of Escherichia coli is compensated by increased enzyme synthesis %D 1996 %J Microbiology, %V 142 %N 2 %P 359-365 %@ 1465-2080 %R https://doi.org/10.1099/13500872-142-2-359 %K RNA analysis %K nucleotide synthesis %K PRPP synthase %K phosphoribosylpyrophosphate %K prs gene %I Microbiology Society, %X 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. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/13500872-142-2-359