Induction and repression of β-galactosidase in non-growing Escherichia coli

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Abstract
Various strains of Escherichia coli deprived of ammonium salts, or of an essential amino acid or pyrimidine, are nevertheless able to produce considerable amounts of induced [beta]-galactosidase in washed suspension. Under non-growing conditions, compounds which the cells can use as sources of carbon and energy repress enzyme formation. The repressors appear to act upon the enzyme-forming system and not upon the galactoside permease. Incorporation of [C14] leucine into protein is unaffected under conditions which prevent [beta]-galactosidase synthesis. Formation of this enzyme thus appears to be unreliable as a guide to the protein-forming ability of the cells. The repression produced by compounds which are metabolized aerobically is reversed by 2:4-dinitrophenol; that produced by compounds metabolized anaerobically is not reversible. The repressor of [beta]-galactosidase appears to be a substance common to aerobic and anaerobic metabolism. Consideration of the kinetics of enzyme synthesis shows that, in the absence of a carbon source, [beta]-galactosidase constitutes about the same fraction of the total protein being synthesized as it does in the growing culture.