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B Magasanik

Publications and source records attributed to B Magasanik.

158 records · Page 9Linked to original sources
PubMed1967

Glucose-lactose diauxie in Escherichia coli.

Growth of Escherichia coli in medium containing glucose, at a concentration insufficient to support full growth, and containing lactose, is diauxic. A mutation in the gene, CR, which determines catabolite repression specific to the lac operon, was found to relieve glucose-lactose but not glucose-maltose diauxie. Furthermore, a high concentration of lactose was shown to overcome diauxie in a CR(+) strain. Studies on the induction of beta-galactosidase by lactose suggested that glucose inhibits induction by 10(-2)m lactose. Preinduction of the lac operon was found to overcome this effect. The ability of glucose to prevent expression of the lac operon by reducing the internal concentration of inducer as well as by catabolite repression is discussed.

Enzyme Induction↗
PubMed1967

Transient repression of the lac operon.

Severe transient repression of constitutive or induced beta-galactosidase synthesis occurs upon the addition of glucose to cells of Escherichia coli growing on glycerol, succinic acid, or lactic acid. Only mutants particularily well adapted to growth on glucose exhibit this phenomenon when transferred to a glucose-containing medium. No change in ribonucleic acid (RNA) metabolism was observed during transient repression. We could show that transient repression is pleiotropic, affecting all products of the lac operon. It occurs in a mutant insensitive to catabolite repression. It is established much more rapidly than catabolite repression, and is elicited by glucose analogues that are phosphorylated but not further catabolized by the cell. Thus, transient repression is not a consequence of the exclusion of inducer from the cell, does not require catabolism of the added compound, and does not involve a gross change in RNA metabolism. We conclude that transient repression is distinct from catabolite repression.

Carbon Isotopes↗
PubMed1966

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.

Carbohydrates↗
PubMedDate not supplied

Regulation of transcription of the glnALG operon of Escherichia coli by protein phosphorylation.

The transcription of glnA, the structural gene for glutamine synthetase in enteric bacteria, is regulated by the phosphorylation and dephosphorylation of an effector protein, NRI. In its phosphorylated form the effector activates the initiation of transcription at promoters specific of sigma 54, rather than the abundant sigma 70. The ability of NRI-phosphate to stimulate the formation of open promoter-sigma 54 RNA polymerase complexes is enhanced by specific binding sites, located in the case of glnA 100 and 130 base pairs upstream from the transcriptional start site. These sites can be moved more than 1000 base pairs upstream or downstream without losing their effectiveness. The phosphorylation and dephosphorylation of NRI-NRI-phosphate is catalyzed by the modulator protein NRII. Its activity is controlled by an intracellular signal, the ratio of glutamine to 2-ketoglutarate, which is generated by glutamine synthetase in response to the environmental stimulus, the availability or lack of ammonia. The signal is transduced to the modulator by means of 2 additional proteins: uridylytransferase and PII.

Bacterial Proteins↗