Nature of the Effector of Catabolite Repression of β-Galactosidase in Escherichia coli

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Abstract
Loomis, William F., Jr. (Massachusetts Institute of Technology, Cambridge, Mass.), and Boris Magasanik . Nature of the effector of catabolite repression of β-galactosidase in Escherichia coli . J. Bacteriol. 92: 170–177. 1966.—Many carbon sources were found to give rise to catabolite repression of β-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 β-galactosidase. Glucose was observed to elicit catabolite repression of β-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 β-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.