Chromosomal location of the gene encoding phosphoribosylpyrophosphate synthetase in Escherichia coli

A mutant of Escherichia coli with a partially defective phosphoribosylpyrophosphate synthetase (ribosephosphate pyrophosphokinase) has been characterized genetically. The genetic lesion causing the altered phosphoribosylpyrophosphate synthetase, prs, was mapped at 26 min on the linkage map by conjugation. Transductional analysis of the prs region established the gene order as purB-fadR-dadR-tre-pth-prs-hemA-trp. Two additional mutations were identified in the mutant: one in gsk, the gene encoding guanosine kinase, and one in lon, conferring a mucoid colony morphology. The contribution of each mutation to the phenotype of the mutant has been evaluated.     

Genetic map location of the Escherichia coli dnaG gene.

The dnaG locus of Escherichia coli K-12 has been mapped at about 60 min on the genetic map by three-factor crosses using P1 transduction. In crosses selecting for dnaG+, the cotransduction frequency with the tolC marker is 15% and that with the uxaC marker is 49%. The gene order is tolC dnaG uxaC.     

Altered acyltransferase activity in Escherichia coli associated with mutations in acyl coenzyme A synthetase

Growth of a temperature-sensitive general fatty acid synthesis mutant of Escherichia coli K12 at its restrictive temperature in the presence of exogenous palmitate results in lysis of the bacterium. Under these conditions, palmitate is incorporated into membrane phospholipid to a high level. Mutants of bacteria restricting this incorporation (having a palmitate-resistant phenotype) have been isolated and one such mutant, strain L8-2/3, has been further characterized. This mutant has lowered acyl-CoA synthetase (fadD) activity (25-33% of normal) and consequently is defective in fatty acid uptake. This lowered uptake could explain the palmitate-resistant phenotype of strain L8-2/3. However, both in vivo (fatty acid composition and positional distribution data) and in vitro (acyltransferase activity measurements) experiments suggest that this mutant is also altered in its acyltransferase activities. The mutation(s) of strain L8-2/3 appears to allow increased (approximately 2-fold) incorporation of myristate (and possible unsaturated fatty acids) into position 2 of 1-acyl-sn-glycerol 3-phosphate but normal palmitate incorporation into the same position. The incorporation of palmitate, myristate, and oleate into position 1 of sn-glycerol 3-phosphate by strain L8-2/3 is also higher than that observed with the parent, strain L8-2. Replacing the partially defective fadD gene of strain L8-2/3 with a wild type allele conferred on this strain the palmitate sensitivity and the acyltransferase activity of the parent strain L8-2. This finding, taken together with other data, suggests that acyl-CoA synthetase interacts with the acyltransferase(s) in some manner to influence the fatty acid specificity of the acyltransferase.     

Regulation of acetyl coenzyme A synthetase in Escherichia coli

Cells of Escherichia coli growing on sugars that result in catabolite repression or amino acids that feed into glycolysis undergo a metabolic switch associated with the production and utilization of acetate. As they divide exponentially, these cells excrete acetate via the phosphotransacetylase-acetate kinase pathway. As they begin the transition to stationary phase, they instead resorb acetate, activate it to acetyl coenzyme A (acetyl-CoA) by means of the enzyme acetyl-CoA synthetase (Acs) and utilize it to generate energy and biosynthetic components via the tricarboxylic acid cycle and the glyoxylate shunt, respectively. Here, we present evidence that this switch occurs primarily through the induction of acs and that the timing and magnitude of this induction depend, in part, on the direct action of the carbon regulator cyclic AMP receptor protein (CRP) and the oxygen regulator FNR. It also depends, probably indirectly, upon the glyoxylate shunt repressor IclR, its activator FadR, and many enzymes involved in acetate metabolism. On the basis of these results, we propose that cells induce acs, and thus their ability to assimilate acetate, in response to rising cyclic AMP levels, falling oxygen partial pressure, and the flux of carbon through acetate-associated pathways.