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A Danchin

Publications and source records attributed to A Danchin.

At least 181 records · Page 10Linked to original sources
PubMed1983

2-Ketobutyrate: a putative alarmone of Escherichia coli.

2-ketobutyrate is synthesized from threonine by threonine deaminase (dehydratase) in E. coli. The effects of 2-ketobutyrate as a regulatory metabolite were studied in vivo. 2-ketobutyrate was shown to inhibit the phosphoenolpyruvate (PEP): sugar phosphotransferase system resulting in aspartate starvation, elevation of ppGpp endogenous pools, and cessation of growth in E. coli grown in glucose and related carbon sources. Accordingly, we propose that 2-ketobutyrate might serve as an alarmone whose concentration precisely governs the shift from anaerobic growth to aerobic growth in E. coli. Such shifts are common phenomena among the Enterobacteriaceae.

Anaerobiosis↗
PubMed1983

Specification of the immune response: its suppression induced by chloramphenicol in vitro.

Specific in vitro PFC responses to trinitrophenyl conjugated to sheep red blood cells are inhibited by chloramphenicol (CAP), thiamphenicol (TAP), and diuron (DIU) by B-cell impairment. However, both mitogenic and polyclonal response to lipopolysaccharide is not affected by CAP and TAP but severely inhibited by DIU. Similarly, contact of cultured cells for the first 24 h with CAP did not much affect the 4th-day in vitro PFC response but the same incubation with DIU reduced it by 70%. Moreover, DIU used at the same concentration provoked an important mortality of cultured cells. These differences suggest that the target mechanism of CAP and TAP differs from that of DIU.

Animals↗
PubMed1983

Vectors for high conditional expression of cloned genes.

Several multicopy plasmids carrying the control region of bacteriophage lambda lysogeny, including the gene of a thermosensitive repressor CI857 have been constructed. The phages allow high expression of proteins under the transcription control of lambda promoter PR and translation control of Cro. The method has been assayed by measuring expression of either intact beta-galactosidase, truncated beta-galactosidase or beta-galactosidase fused to a mitochondrial gene product. It is shown that use of a strain with low endogeneous proteolytic activities strongly improves the conditional yield of foreign proteins, so that a high overproduction can be achieved (10-20 per cent of the total protein content of the cell).

Bacteriophage lambda↗
PubMed1982

The cya locus of Escherichia coli K12: organization and gene products.

The cya gene region of Escherichia coli K12 has been cloned into plasmid pBR322. Detailed analysis of the locus, using in vitro recombination techniques as well as specific labelling of gene products has given information on the organization and products of the region. The cya gene is preceded by two DNA segments which behave as promoters of equivalent strength; a divergent, very strong, promoter is also present in the same control region. The former pair of promoters direct transcription of the cya gene which is expressed as a 95,000 dalton polypeptide; the latter promoter controls synthesis of a 40,000 dalton polypeptide. The cya gene product can complement a cya delta mutation when fully expressed or when expressed as a protein truncated at its carboxy terminal end.

Bacterial Proteins↗
PubMed1981

[A biochemical mechanism for the epigenesis of the neuromuscular junction].

A biochemical mechanism, expressed as a system of diffusion equations with non linear coupling on the muscle membrane, quantitatively accounts for the development of the neuromuscular junction and for the epigenetic dependence on the afferent multimessages of the focal and distributed synaptic topologies.

Models, Biological↗
PubMed1981

Generation of immune specificity: a working hypothesis.

A speculative model for epigenetic generation of immune specificity is presented. It is based on the idea that combinatorial splicing within the same pre-mRNA molecule could generate a variety o mRNAs leading to a diversity of immunoglobulins. The model postulates a special role for the nuclear envelope where translation of intron sequences into messenger maturation proteins would take place. The postulates are justified and experimental implications of the model are discussed.

Epitopes↗
PubMed1981

Transcription-translation coupling and polarity: a possible role of cyclic AMP.

Using specific mutants exhibiting altered translational rates we found that when the rate of protein synthesis is reduced the polarity of the lactose and galactose operons is increased. This polarity is in part relieved by cyclic AMP. On the basis of in vitro hybridization experiments were propose that the cyclic AMP-CAP complex and the ribosomes display similar functions, namely destabilization of the RNA-DNA hybrid formed during transcription.

Bacteria↗
PubMed1981

Regulation of galactose operon expression: glucose effects and role of cyclic adenosine 3',5'-monophosphate.

We studied the following two aspects of the glucose effect on galactose operon expression in Escherichia coli K-12: catabolite repression and inducer exclusion. Using both inducible and constitutive strains and measuring the rate of promoter-proximal enzyme synthesis, we found that the galactose operon did not seem to exhibit catabolite repression. The only glucose effect on galactose operon expression which we observed was inducer exclusion, as shown by the existence of diauxic growth in the presence of glucose and galactose. This diauxie was not relieved by cyclic adenosine 3',5'-monophosphate. Cyclic adenosine 3',5'-monophosphate did not seem to be an antagonist of any glucose effect on galactose operon expression; its only effect was to stimulate promoter-distal gene expression.

Cyclic AMP↗
PubMed1981

Isolation and characterization of an Escherichia coli mutant affected in the regulation of adenylate cyclase.

A mutant, cyaR1, affecting regulation of adenylate cyclase expression or activity is described. It was obtained as a thermoresistant revertant of a strain harboring a thermosensitive transcription termination factor, rho (rho-15). This mutant failed to synthesize adenosine 3',5'-phosphate and exhibited a carbohydrate-negative phenotype. A secondary mutation at the crp locus (crpC) restored the ability of the mutant to synthesize adenosine 3',5'-phosphate, enabled the expression of catabolite-sensitive operons, and conferred on the strain an extreme sensitivity to catabolite repression. In addition, we showed that the crpC mutation restored the pleiotropic carbohydrate-positive phenotype even in a delta cya background. We interpret this to mean that the adenosine 3',5'-phosphate receptor protein regulates negatively either the activity or synthesis of adenylate cyclase and that the cyaR1 mutation is either in a regulatory protein or a regulatory site of adenylate cyclase.

Adenylyl Cyclases↗
PubMed1980

Serine sensitivity of Escherichia coli K 12: partial characterization of a serine resistnat mutant that is extremely sensitive to 2-ketobutyrate.

E. coli wild type bacteria display sensitivity towards serine. A selection medium is described which allows selection of serine resistant mutants. One such mutant is described which presents pleiotropic alterations: it exhibits a thermosensitive growth pattern, alteration in the metabolism of the pppGpp and ppGpp nucleotides, cAMP intracellular level alteration, extreme sensitivity to 2-ketobutyric acid and a defect in the phosphotransferases permeation system. A conjecture explaining these apparently unrelated defects supposes that serine metabolism interferes via phosphoenol pyruvate with a cytoplasmic control of membrane activity (the mutant would be defective in the coupling between membrane and the protein responsible for its cytoplasmic control) and that 2-ketobutyrate is an effector of this activity.

Butyrates↗
PubMed1980

Catabolite repression in Escherichia coli mutants lacking cyclic AMP receptor protein.

Pleiotropic carbohydrate-positive pseudorevertants have been isolated from a specific class of rho-crp double mutants of Escherichia coli carrying both defective transcription termination protein, rho, and cyclic AMP receptor protein. The modulation of catabolite repression of beta-galactosidase, amylomaltase, and tryptophanase has been studied in the pseudorevertants. It has been found that these mutants exhibit catabolite repression. Because catabolite-sensitive operons can be expressed in the absence of functional cyclic AMP receptor protein, this would suggest on the one hand that the cyclic AMP-receptor protein complex is not the exclusive mediator of catabolite repression and on the other hand that rho might be involved in the regulation of catabolite-sensitive operons.

Cyclic AMP↗
PubMed1979

On the binding of tRNA to Escherichia coli RNA polymerase.

The fixation of tRNA to Escherichia coli RNA polymerase has been investigated. Bound and free tRNA have been separated and quantified after filtration through cellulose nitrate filters, centrifugation or sucrose gradients or electrophoresis in polyacrylamide gels. We detect no differences between the fixation of E. coli fMet-tRNAfMet, Met-tRNAmMet or uncharged unfractionated tRNA to RNA polymerase. Tight complexes, with a long residence time, are formed between core enzyme and tRNA with a dissociation constant of less than 1 nM. Complexes exist between tRNA and both monomer and dimer forms of the core enzyme. In the monomer complex, one tRNA is bound per alpha 2 beta beta' unit, whereas in the dimer complex only 0.5 tRNA molecule is fixed per alpha 2 beta beta' unit. In contrast to the core enzyme, very little tRNA fixes tightly to the holoenzyme at salt concentrations greater than 80 mM. At lower salt concentrations tRNA fixation results in a loss of sigma subunit from the holo enzyme to the resulting core enzyme where it binds tightly. DNA fixation reduces the binding of tRNA to RNA polymerase and tRNA fixation reduces the binding of DNA. However, binding of DNA to polymerase is not competitive with binding of tRNA, and ternary complexes between RNA polymerase, DNA and tRNA are shown to exist. Our results are discussed in relation to other studies concerning the effects of tRNA upon RNA polymerase.

DNA↗
PubMed1979

Involvement of cyclic AMP and its receptor protein in the sensitivity of Escherichia coli K 12 toward serine: excretion of 2-ketobutyrate, a precursor of isoleucine.

A relationship between serine-induced growth sensitivity and the cAMP-CAP complex is established. Mutants of Escherichia coli K 12 deficient either in the cya or crp gene function exhibit a resistant phenotype on serine media although they harbor a relA allele normally leading to sensitivity toward serine. The presence of a crp allele in a cya delta relA background restores the sensitivity phenotype, while the analysis of serine resistant mutants selected from a crp cya delta relA strain shows that the mutation leading to resistance is located at, or very near, the crp gene, giving a more or less Crp- phenotype. In addition crp cya delta relA strains excrete large quantities of 2-ketobutyrate when grown on glucose M63 medium. This excretion is unambiguously linked to the presence of the crp allele and is correlated with an enhanced threonine deaminase activity. Besides, the complex regulation exerted on the acetolactate synthase activities is discussed.

Butyrates↗