The roles of inducer and catabolite repressor in the synthesis of β-galactosidase by Escherichia coli

The regulatory process in the de-repression of enzyme synthesis. Alkaline phosphatase of Bacillus subtilis

1. The kinetics of de-repression of alkaline phosphatase in Bacillus subtilis were studied after the removal of P(i). Enzyme activity appeared about 10min. after removal of P(i), whereas ;enzyme-forming potential' appeared after 6min. 2. Protein synthesis is not impaired for at least 20min. on removal of P(i), but RNA synthesis is considerably diminished. 3. Adding chloramphenicol to cells without P(i), just at the time they start to make enzyme-forming potential, does not affect the differential rate of enzyme synthesis compared with total protein. Enzyme-forming potential accumulates to about normal levels in the presence of chloramphenicol, even though peptide-bond formation is inhibited by more than 95%. 4. Similar experiments performed with actinomycin C show more complex effects. Actinomycin initially prevents RNA synthesis and also the synthesis of enzyme-forming potential. After some minutes RNA synthesis resumes at a low rate, to be followed 4min. later by enzyme synthesis. Enzyme-forming potential can accumulate in the presence of actinomycin after the resumption of RNA synthesis. Protein synthesis, initially inhibited by actinomycin as a consequence of the effect on RNA synthesis, is later directly inhibited by actinomycin. 5. Adding actinomycin to de-repressed cells already making enzyme stops enzyme synthesis within 4-5min. Enzyme synthesis resumes, as before, 4min. after the resumption of RNA synthesis. 6. Adding P(i) together with actinomycin to de-repressed cells synthesizing enzyme does not result in a lower yield of enzyme compared with actinomycin alone. 7. Actinomycin is less effective an inhibitor of RNA and protein synthesis in P(i)-starved cells if P(i) is also added. 8. These results are discussed in view of the three main models for the regulation of enzyme induction: regulation at the level of transcription only, at translation only, or a coupled model in which transcription requires concomitant translation. It is concluded that the present evidence most powerfully supports the model of transcriptional regulation.

Pool sizes of metabolic intermediates and their relation to glucose repression of beta-galactosidase synthesis in Escherichia coli

1. The intermediary metabolism of two strains of Escherichia coli has been examined. One strain (Q22) exhibits acute transient repression of beta-galactosidase synthesis when glucose is supplied to cells growing on glycerol; the other strain (W3110) does not. The two strains do not differ genetically in their lac operons. 2. Strain Q22 uses about twice as much glucose as strain W3110 per unit of cell mass produced. 3. Pentose phosphate-cycle activity in the presence of glucose is much stronger in strain Q22 than in strain W3110. 4. In strain Q22 the pool sizes of glucose 6-phosphate, 6-phosphogluconate, fructose 1,6-diphosphate and NADPH increase when glucose is added to cells growing on glycerol, and beta-galactosidase synthesis is severely inhibited. After about 1hr. the synthesis of beta-galactosidase is partly resumed, and the pool sizes of the four compounds fall. ATP, NADH and several other phosphorylated compounds show no concentration changes. 5. These concentration changes do not occur in strain W3110, in which beta-galactosidase synthesis is only rather weakly repressed by glucose. 6. It is suggested that repression of enzyme synthesis by glucose requires the rapid operation of the pentose phosphate cycle, and is mediated by one of the four substances whose concentration rises and later falls in strain Q22. A definite choice of effector from among these four possibilities cannot at present be made.

Catabolite repression and pyruvate metabolism in Escherichia coli

A study was made of the reactions involved in the cellular regulatory function known as catabolite repression. These studies employed the glucose-repressible, beta-galactosidase system of Escherichia coli and involved an investigation of glucose dissimilation under cultural conditions capable of permitting or preventing expression of catabolite repression. The results indicated that reactions associated with pyruvate decarboxylation are of particular importance in influencing repression. This conclusion was based on results obtained by measurement of differential rates of C(14)O(2) evolution from specifically labeled (14)C-glucose substrates, and by measurements of H(2) evolution during anaerobic growth. Catabolite repression measured in relation to steady-state growth rates indicated that the repression mechanism may in fact be a direct consequence of a cell's energy balance, as dictated by the production from pyruvate of "high-energy" molecules such as adenosine triphosphate or acetyl-coenzyme A. The apparent involvement of pyruvate metabolism in both the energetics and the expression of catabolite repression in E. coli is consistent with this view.

Involvement of the lac regulatory genes in catabolite repression in Escherichia coli

1. Acute transient catabolite repression of beta-galactosidase synthesis, observed when glucose is added to glycerol-grown cells of Escherichia coli (Moses & Prevost, 1966), requires the presence of a functional operator gene (o) in the lactose operon. Total deletion of the operator gene abolished acute transient repression, even in the presence of a functional regulator gene (i). 2. Regulator constitutives (i(-)) also show transient repression provided that the operator gene is functional. Regulator deletion mutants (i(del)), with which to test specifically the role of the i gene, have not so far been available. 3. The above mutants, showing various changes in the lactose operon, show no alteration in the effect of glucose on induced tryptophanase synthesis. Glucose metabolism, as measured in terms of the release of (14)CO(2) from [1-(14)C]glucose and [6-(14)C]glucose, also showed no differences between strains exhibiting or not exhibiting transient repression. This suggests no change in the operation of the pentose phosphate cycle, a metabolic activity known to be of paramount importance for glucose repression of beta-galactosidase synthesis (Prevost & Moses, 1967). 4. Chronic permanent repression by glucose of beta-galactosidase synthesis (less severe in degree than acute transient repression) persists in strains in which transient repression has been genetically abolished. Constitutive alkaline-phosphatase synthesis, which shows no transient repression, also demonstrates chronic permanent repression by glucose. 5. Chloramphenicol repression also persists in mutants with no transient repression, and also affects alkaline phosphatase. It is suggested that chronic permanent repression and chloramphenicol repression are non-specific, and that they do not influence beta-galactosidase synthesis via the regulatory system of the lactose operon.

Mechanisms of regulation of urease biosynthesis in Proteus rettgeri

Urease of Proteus rettgeri is an inducible enzyme synthesized specifically in the presence of urea; urea analogues did not act as inducers. Once initiated, the biosynthesis of the enzyme proceeded as a constant fraction of the total protein formed. The rate of urease formation was affected by the carbon source used. In comparison with glycerol, glucose inhibited enzyme synthesis. The addition of ammonium ions to the inducing medium also decreased the rate of urease biosynthesis, and when ammonium ions were present urease activity and urea transport across the cell membrane were inhibited. A kinetic analysis of urease inhibition by ammonium ions, by use of a partially purified preparation of urease, showed that it was a competitive inhibition.

Heterogeneity of the stability of messenger ribonucleic acid in Salmonella typhimurium

Cells of Salmonella typhimurium strain SL 282, deflagellated by mechanical shear, regenerated their flagella in the absence of tryptophan, an amino acid required for growth but not found in flagellin. Ribonucleic acid (RNA) synthesis was severely inhibited by tryptophan starvation. These findings suggested that the messenger RNA (mRNA) for flagellin might be stable. Actinomycin D was used to inhibit RNA synthesis in ethylenediaminetetraacetate-treated bacteria. The introduction of an F(lac) episome into strain SL 282 permitted the simultaneous study of the synthesis of flagellin, beta-galactosidase, and total protein. In the actinomycin-treated bacteria protein and beta-galactosidase syntheses were inhibited by 90%, whereas flagellin synthesis was unaffected. We conclude that the mRNA for flagellin synthesis is stable and that species of mRNA vary with respect to metabolic stability in S. typhimurium.

Catabolite repression of beta-galactosidase synthesis in Escherichia coli

1. Repression by glucose of beta-galactosidase synthesis is spontaneously reversible in all strains of Escherichia coli examined long before the glucose has all been consumed. The extent of recovery and the time necessary for reversal differ among various strains. Other inducible enzymes show similar effects. 2. This transient effect of glucose repression is observed in constitutive (i(-)) and permease-less (y(-)) cells as well as in the corresponding i(+) and y(+) strains. 3. Repression is exerted by several rapidly metabolizable substrates (galactose, ribose and ribonucleosides) but not by non-metabolized or poorly metabolized compounds (2-deoxyglucose, 2-deoxyribose, phenyl thio-beta-galactoside and 2-deoxyribonucleosides). 4. The transient repression with glucose is observed in inducible cells supplied with a powerful inducer of beta-galactosidase synthesis (e.g. isopropyl thio-beta-galactoside) but not with a weak inducer (lactose); in the latter instance glucose repression is permanent. Diauxic growth on glucose plus lactose can be abolished by including isopropyl thio-beta-galactoside in the medium. 5. In some strains phosphate starvation increases catabolite repression; in others it relieves it. Adenine starvation in an adenine-requiring mutant also relieves catabolite repression by glycerol but not that by glucose. Restoration of phosphate or adenine to cells starved of these nutrients causes a pronounced temporary repression. Alkaline-phosphatase synthesis is not affected by the availability of adenine. 6. During periods of transient repression of induced enzyme synthesis the differential rate of RNA synthesis, measured by labelled uracil incorporation in 2min. pulses, shows a temporary rise. 7. The differential rate of uracil incorporation into RNA falls during exponential growth of batch cultures of E. coli. This is equally true for uracil-requiring and non-requiring strains. The fall in the rate of incorporation has been shown to be due to a real fall in the rate of RNA synthesis. The significance of the changes in the rate of RNA synthesis is discussed. 8. A partial model of catabolite repression is presented with suggestions for determining the chemical identification of the catabolite co-repressor itself.

Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli

Loomis, William F., Jr. (Massachusetts Institute of Technology, Cambridge, Mass.), and Boris Magasanik. Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli. J. Bacteriol. 92:170-177. 1966.-Many carbon sources were found to give rise to catabolite repression of beta-galactosidase in a mutant strain of Escherichia coli lacking hexose phosphate isomerase activity. Compounds containing glucose or galactose cannot be formed from several of these carbon sources in this mutant strain, and, therefore, appear not to be required for catabolite repression of beta-galactosidase. Glucose was observed to elicit catabolite repression of beta-galactosidase in another mutant strain under conditions in which the formation of compounds of the citric acid cycle is inhibited. If catabolite repression of the lac operon is mediated by a single compound, it appears that the compound is related to the pentoses and trioses of intermediary metabolism. The repression of beta-galactosidase by galactose in galactokinase negative strains was shown to be independent of the gene, CR, which determines catabolite sensitivity of the lac operon, and to be dependent on a functional i gene.

Galactose repression of beta-galactosidase induction in Escherichia coli

Beggs, William H. (University of Minnesota, Minneapolis), and Palmer Rogers. Galactose repression of beta-galactosidase induction in Escherichia coli. J. Bacteriol. 91:1869-1874. 1966.-Galactose repression of beta-galactosidase induction in Escherichia coli was investigated to determine whether the galactose molecule itself is the catabolite repressor of this enzyme system. Without exception, beta-galactosidase induction by cells grown in a synthetic salts medium with lactate or glycerol as the carbon source was more strongly repressed by glucose than by galactose. This relationship existed even when the organism was previously grown in the synthetic medium containing galactose as the source of carbon. Two observations suggested that the ability of galactose to repress beta-galactosidase formation by Escherichia coli depends directly upon the cells' capacity to catabolize galactose. First, galactose repression of beta-galactosidase synthesis was markedly enhanced in bacteria tested subsequent to gratuitous induction of the galactose-degrading enzymes with d-fucose. Second, galactose failed to exert a repressive effect on beta-galactosidase in a galactose-negative mutant lacking the first two enzymes involved in galactose catabolism. Glucose completely repressed enzyme formation in this mutant. This same mutant, into which the genes for inducible galactose utilization had been introduced previously by transduction, again exhibited galactose repression. Pyruvate was found to be at least as effective as galactose in repressing beta-galactosidase induction by cells grown in synthetic salts medium plus glycerol. It is concluded that the galactose molecule itself is not the catabolite repressor of beta-galactosidase, but that repression is exerted through some intermediate in galactose catabolism.

Action of phyenethyl alcohol on the synthesis of macromolecules in Escherichia coli

Prevost, C. (University of California, Berkeley), and V. Moses. Action of phenethyl alcohol on the synthesis of macromolecules in Escherichia coli. J. Bacteriol. 91:1446-1452. 1966.-A kinetic study of the effects of various concentrations of phenethyl alcohol on the synthesis of ribonucleic acid (RNA), deoxyribonucleic acid (DNA), protein, and beta-galactosidase in Escherichia coli has confirmed that RNA synthesis, rather than DNA synthesis, is first and most affected by phenethyl alcohol. The presence of inducer did not protect beta-galactosidase synthesis from inhibition by phenethyl alcohol. Little preferential inhibition of beta-galactosidase synthesis was observed; this is in contrast to the severe catabolite repression which results from partial inhibition of total protein synthesis caused by chloramphenicol or starvation for a required amino acid. We found no evidence that messenger RNA synthesis was inhibited to a greater extent than total RNA synthesis.