NEGATIVE DOMINANT MUTATIONS OF THE uidR GENE IN ESCHERICHIA COLI: GENETIC PROOF FOR A COOPERATIVE REGULATION OF uidA EXPRESSION

Abstract

The uidA gene is the first gene involved in the hexuronide-hexuronate pathway in Escherichia coli K-12 and is under the dual control of the uidR and uxuR encoded repressors. Point mutations affecting the uidR regulatory gene were sought to investigate the regulation of uidA. When the uidR mutant allele was on a multicopy plasmid and the wild-type allele was on the chromosome, some of the mutant phenotypes were dominant to the wild-type phenotype, indicating that the active form of the UidR repressor is multimeric. We have demonstrated that expression of the mutant phenotype is dependent on gene dosage. The dominance of the uidR allele was also sensitive to the presence of the wild-type uxuR allele in the cell. This behavior probably results from UidR-UxuR repressor interactions. A mechanism is proposed: we suggest that the UidR and UxuR repressors interact after their binding to the operator site of uidA; the binding of one regulatory molecule may facilitate the binding of the other one in a cooperative process.

Increasing Extracellular Free Fatty Acid Production in Escherichia coli by Disrupting Membrane Transport Systems

“…The outer membrane porin GusC is known to be responsible for uptake of β-glucuronides . Expression of GusC is induced by two types of effector molecules, namely glucuronate (a sugar acid derived from glucose) and β-glucuronides (compounds synthesized by linking glucuronate to another substance via a glycosidic bond) . GusC expression has been shown to decline during cell transition from the exponential phase to the stationary phase .…”

“…34 Expression of GusC is induced by two types of effector molecules, namely glucuronate (a sugar acid derived from glucose) and β-glucuronides (compounds synthesized by linking glucuronate to another substance via a glycosidic bond). 35 GusC expression has been shown to decline during cell transition from the exponential phase to the stationary phase. 36 This protein has homology to the Occ (outer membrane carboxylate channels) family, which requires substrates with carboxyl groups for efficient import.…”

Differential Impact of Hexuronate Regulators ExuR and UxuR on the Escherichia coli Proteome

“…Together, they control genes encoding all key enzymes for hexuronate utilisation, specifically, oxidoreductase UxuB and mannonate dehydratase UxuA, glucuronidase UidA, glucuronate/galacturonate isomerase UxaC, hexuronate transporters ExuT and GntP, and glucuronide transporters UidB and UidC. Moreover, both regulators serve as autorepressors [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. Initially, UxuR was believed to be responsible for the expression of all genes coding for enzymes and transporters related to glucuronate metabolism [ 5 , 7 , 9 ], while ExuR—for galacturonate metabolism [ 2 , 3 , 6 , 7 ].…”

Differential Impact of Hexuronate Regulators ExuR and UxuR on the <em>Escherichia coli</em> Proteome

“…Together, they control genes encoding all key enzymes for hexuronate utilisation, specifically, oxidoreductase UxuB and mannonate dehydratase UxuA, glucuronidase UidA, glucuronate/galacturonate isomerase UxaC, hexuronate transporters ExuT and GntP, and glucuronide transporters UidB and UidC. Besides, both regulators serve as autorepressors [1][2][3][4][5][6][7][8][9][10][11][12] Initially, UxuR was believed to be responsible for all enzymes and transporters related to glucuronate metabolism [5,7,9], while ExuRfor galacturonate metabolism [2,3,6,7]. Later, ExuR and UxuR were shown to cross regulate each other targets, probably forming heterodimers [10][11].…”

“…Besides, both regulators serve as autorepressors [1][2][3][4][5][6][7][8][9][10][11][12] Initially, UxuR was believed to be responsible for all enzymes and transporters related to glucuronate metabolism [5,7,9], while ExuRfor galacturonate metabolism [2,3,6,7]. Later, ExuR and UxuR were shown to cross regulate each other targets, probably forming heterodimers [10][11]. Interchangeability of D-galacturonate and D-glucuronate as effectors and heterodimer formation was further confirmed in [12].…”