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J Bacteriol. 1969 March; 97(3): 1083-1092
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Corepressor System for Catabolite Repression of the lac Operon in Escherichia coli¹

^a Department of Microbiology, North Carolina State University, Raleigh, North Carolina 27607

ABSTRACT

Acetylated amino sugars, normally used in the biosynthesis of cell walls and cell membranes, were found to play a role as corepressors for catabolite repression of the lac operon in Escherichia coli. This conclusion was derived from studies conducted on mutants of E. coli that were able to assimilate an exogenous source of N-acetylglucosamine (AcGN) but were unable to dissimilate or grow on this compound. At concentrations less than 10^–4M, AcGN caused severe catabolite repression of ß-galactosidase synthesis in cultures grown under either nonrepressed or partially repressed conditions. This repression occurred in the absence of any effect of AcGN on either the carbon and energy metabolism or the growth of the organism. In addition, this repression by AcGN occurred in a mutant strain that is constitutive for ß-galactosidase production, demonstrating that the AcGN effect does not involve the uptake of inducer. This model for the corepressor system of catabolite repression is discussed in relation to the existing theories on repression of the lac operon.

¹ Paper number 2656 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, N.C.