title: Synthesis and turnover of basal level guanosine tetraphosphate in Escherichia coli.
abstract: Cultures of escherichia coli growing exponentially in Trisacetate medium were subjected to nutritional shift-up and the pool size of guanosine 5'-3'-diphosphate-3'diphosphate (ppGpp) as well as the rates of protein synthesis and net RNA synthesis were determined. In the shift to a rich medium (glucose plus 19 amino acids plus hypoxanthine) the basal level of ppGpp falls immediately with a decay constant suggesting total inhibition of synthesis; ther is no ppGpp detectable above background for 30 to 40 min. The net rate of RNA synthesis starts to increase within 1 min of the shift-up and has reached its definite postshift value well before the pool of ppGGpp rises above background lvel. In a shift-up from Tris-acetate medium to Tris-glucose medium there is a much slower readjustment of the ppGpp pool size without the transient disappearance of the nucleotide. However, in a shift-up to Tris-acetate plus 5 amino acids, a medium which supports the same growth rate as Tris-glucose medium, a dramatic, transient drop in the ppGpp pool level was observed. Relaxed cells exhibit very similar behavior to strigent cells in the same shift-up. Our data argue strongly against an exclusive role for pGpp in regulating RNA synthesis during niutritional shift-up. The kinetic data of [3H]guanosine uptake into GTP and ppGpp pools were analyzed to determine the rate of pGpp synthesis. This rate was found to be similar during expotential growth in either Tris-acetate medium. During a shift-down from Tris-glucose to Tris-acetate medium the rate of ppGpp syntesis fell by a factor of 1.5 to 2 and the turnover rate is reduced 6- to 8-fold, suggesting that the expansion in the ppGp pool during shift-down canot be due to derepression of synthesis.
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis; D002250:Carbon Radioisotopes; D002455:Cell Division; D003470:Culture Media; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000096:biosynthesis / Q000378:metabolism*; D006151:Guanosine / Q000378:metabolism; D007553:Isotope Labeling; D007930:Leucine / Q000378:metabolism; D009154:Mutation; D010761:Phosphorus Radioisotopes; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000096:biosynthesis; D012265:Ribonucleotides / Q000096:biosynthesis; D013997:Time Factors; D014158:Transcription, Genetic; D014316:Tritium; D014325:Tromethamine / Q000494:pharmacology; D014498:Uracil / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D003470:Culture Media; D006150:Guanine Nucleotides; D010761:Phosphorus Radioisotopes; D012329:RNA, Bacterial; D012265:Ribonucleotides; D014325:Tromethamine; D014316:Tritium; D006151:Guanosine; D014498:Uracil; D007930:Leucine; D005947:Glucose