Figure 4

With the exception of ppGpp, the levels of nucleotides are stable in E. coli throughout the growth curve. (a) Intracellular nucleotides of E. coli cultures grown in defined minimal medium (MOPS 0.4% glc at 37 °C with vigorous aeration) are expressed as ratios of guanosine, adenosine, and NTP pools as indicated in the insert. AEC refers to the adenylate energy charge defined by Atkinson⁷. Cells were harvested by filtration and nucleotides extracted with acetic acid. ppGpp was measured using isocratic SAX and the remaining nucleotide species were quantified using gradient IPRP. GMP was not resolved using IMP and the earliest feasible sampling point was at an OD₆₀₀ of 0.3. (b) Intracellular nucleotide levels are expressed as absolute concentrations. The cell volumes used to convert from nucleotide ratios to absolute concentrations were estimated using a method provided in Supplementary Methods. Error bars indicate the standard error of the mean of biological replicates (n = 7).