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The effect of trimethoprim on macromolecular synthesis in Escherichia coli. Regulation of ribonucleic acid synthesis by 'Magic Spot' nucleotides.

ABSTRACT: During the inhibition of RC(str), but not RC(rel) mutants of Escherichia coli by trimethoprim the unusual nucleotides MSI (guanosine tetraphosphate, ppGpp) and MSII rapidly accumulated. The production of these nucleotides was not dependent on the addition of nucleotide base supplements to RC(str) cultures before trimethoprim, and the MSI nucleotide concentrations in non-supplemented or purine-supplemented cultures were comparable with the concentrations obtained when the cells were inhibited with l-valine (1g/l). Rifampicin rapidly decreased MSI and MSII nucleotide concentrations in trimethoprim-inhibited cultures to the basal values. Several situations were noted, in which MS nucleotide concentrations in trimethoprim-inhibited RC(str) cells could be drastically lowered without giving rise to an immediate resumption of stable RNA accumulation. If RC(str) mutants were first inhibited with trimethoprim and then given purines 15min later, MS nucleotide concentrations fell rapidly, because of a temporarily enhanced rate of accumulation of stable RNA. However, after a further 5min, RNA accumulation stopped, though MS nucleotide concentrations remained low. Also, if either glycine or methionine were added to trimethoprim-inhibited cultures supplemented with purines, RNA accumulation did not resume, though MS nucleotide concentrations rapidly declined. With both amino acids present, there was both a decline in MS nucleotide concentration and a resumption in stable RNA synthesis. These findings suggest that MSI nucleotide concentrations in trimethoprim-inhibited bacteria are not the sole factors in the control of stable RNA synthesis. It is possible that, during the period when the RC(str) cells contained high concentrations of MS nucleotides, some factor important in the MSI-mediated control of stable RNA synthesis was irreversibly inactivated. However, as antibiotics (e.g. chloramphenicol) both abolished high MS nucleotide concentrations and permitted a rapid resumption of stable RNA accumulation in the same conditions, it is more likely that an additional control mechanism has come into play.

SUBMITTER: Smith RJ

PROVIDER: S-EPMC1165950 | biostudies-other | 1973 Oct

REPOSITORIES: biostudies-other

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Project description:When Escherichia coli was inhibited with trimethoprim in media supplemented with nucleotide bases, glycine and methionine, both RC(str) and RC(rel) strains continued to accumulate RNA at rates very close to those in growing controls. The effects of trimethoprim on protein synthesis were studied by using as an experimental basis the rate of maturation of ribosomal particles from RNA-rich precursors. 1. In RC(str) cultures given nucleotide bases but no amino acids, RNA accumulation was inhibited because of amino acid lack. However, maturation of ribosomes from their precursors was more severely inhibited than was the synthesis of rRNA. The restraints on protein synthesis were more severe at the level of translation than the transcription of operons specific for the formation of ribosomal proteins. The kinetic delay time in the passage of rRNA from RNA-rich intermediates to the final ribosome products was therefore increased some three- to four-fold. 2. In RC(rel) cultures in the same conditions, trimethoprim inhibition stopped ribosomal particle synthesis, but rRNA-rich precursors accumulated. 3. If glycine+methionine were also added to inhibited RC(str) cultures, RNA accumulation resumed at a high rate. However, ribosomal maturation was still considerably disturbed because of a disproportionate response of the cells in the formation of protein and RNA. 4. With RC(rel) cultures, addition of the amino acids caused a large increase in the rate of ribosome maturation, though the degree of disproportionation between the rates of rRNA and ribosomal protein synthesis was now identical with that found in RC(str) strains. 5. When inhibited RC(rel) cultures were supplemented, there was still a severe inhibition of protein synthesis at the level of chain initiation, but inaccuracies in the process of polypeptide chain elongation were greatly decreased. This suggests that the effects of the RC(rel) mutation on the fidelity of protein synthesis in bacteria are not directed at the point of chain initiation.

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The effect of trimethoprim on macromolecular synthesis in Escherichia coli. Regulation of ribonucleic acid synthesis by 'Magic Spot' nucleotides.

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