SUMMARY: A newly devised method to obtain diffuse growth of A3(2) in liquid minimal medium was used to study glucose repression. Although diauxic growth was not obtained, glucose repression of uptake of C-labelled carbon sources was demonstrated. Active, arabinose-induced, arabinose transport was repressed at the level of transcription by glucose. Of two glycerol-inducible glycerol transport systems, one was glucose-inhibited but not repressed (and operated by facilitated diffusion), whilst the other (an active transport system) was glucose-repressed. Active transport systems for galactose and fructose which did not require induction by their respective sugars were both inhibited by glucose. Galactose- and fructose-metabolizing enzymes were inducible by the respective sugars, but only in the absence of glucose. This was because glucose both inhibited galactose and fructose transport and repressed the metabolic enzymes concerned. Constitutive active glucose uptake was also demonstrated in arabinose-grown cells. Mutants that grew on arabinose or glycerol in the presence of 2-deoxy-glucose were glucose-derepressed for both soluble carbon source utilization and extracellular agarose. Three glucose-derepressed mutants were studied in detail. One of these could not utilize glucose (and probably lacks glucose kinase), whilst the other two could utilize glucose to differing degrees.


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