Studies on the repression of β-galactosidase in Escherichia coli

The mechanism of catabolite repression has been tested in mutants of Escherichia coli and a mutant of Aerobacter aerogenes, JF-4, using the technique of nutrient limitation. Two distinct types of enzyme control have been identified: (1) a control which is antagonized by inducer and is called “inducer-specific repression”; and (2) a control which is independent of the concentration of inducer and is called “inducer-independent represseion”. A metho of analysis is employed which allows each of the two types of repression to be measured quantitavely. The restriction of catabolic activities leads to derepression while the restriction of anabolic activities leads to repression; however, the relative change in inducer-specific and inducer-independent repression are not the same. Carbon limitation leads to a preferential decrease in inducer-specific repression while nitrogen and sulfur limitation lead to a preferential increase in inducer-independent repression.