Abstract
The ATP and GTP pools of Escherichia coli have recently been reported to increase approximately 10-fold with increasing growth rates in the range from 0.4 to 1.4 generations/hour (Gaal, T., Bartlett, M. S., Ross, W., Turnbough, C. L., and Gourse, R. L. (1997) Science 278, 2092-2097). Moreover, it was proposed that this variation of the nucleotide pools, particularly the ATP pool, might be responsible for the well known growth rate-dependent regulation of rRNA synthesis in E. coli. To test this hypothesis we have measured the nucleoside triphosphate pools as a function of growth rate for several E. coli strains. We found that the size of all four RNA precursor pools are essentially invariant with growth rate, in the range from 0.5 to 2.3 generations/hour. Nevertheless we observed the expected growth rate-dependent increase of RNA accumulation in these strains. In light of these results, it seems unlikely that nucleotide pool variations should be responsible for the growth rate-dependent regulation of rRNA synthesis.
Highlights
It has been known for more than 30 years that the ribosome content of bacterial cells increases with increasing growth rates, governed by regulatory mechanisms which adjust the rate of ribosome biosynthesis to match the available resources present in the growth medium
Effect of Growth Rate on the nucleoside triphosphate (NTP) Pools—In connection with studies of nucleotide metabolism in RNase-deficient strains we found that the nucleotide pools in a wild type control strain, CN1539, were not increased by supplementation of glycerol minimal medium with all 20 amino acids, even though the amino acid enrichment more than doubled the growth rate (Fig. 1a)
We found that the ATP and GTP pools were essentially constant for growth rates between 0.4 and 1.9 generations/h, if the growth medium was supplemented with uracil
Summary
The bacterial strains used in this study are all derivatives of E. coli K12. CN1539 —ara ⌬(gpt-pro-lac) thi zce-726::Tn10/FЈ(gptϩ proABϩ codABϩ lacIq1 lacZ::Tn5) is the wild type member of an isogenic rneϩ/ rne3071 strain pair, which was constructed by P1-mediated transduction of zce-726::Tn10 from CH1826 [6] into CSH26 [7]. The FЈ factor, which complements the ⌬(gpt-pro-lac) deletion, was subsequently introduced by conjugation with NF1829 [8]. CN1709 —FϪ ara ⌬(codB-lac) thi, is a derivative of CSH26, in which the ⌬(gpt-pro-lac) deletion has been replaced by the shorter ⌬(codB-lac) deletion, known as ⌬(lac)X74, from NF1829. MG1655—FϪ rph1 [9] was obtained from Dr K. CF7968 —FϪ ⌬(lacIZ) is an rphϩ derivative of MG1655, kindly provided by Dr M.
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