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Journal of Bacteriology, March 2004, p. 1720-1728, Vol. 186, No. 6
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.6.1720-1728.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Regulation of Expression of the Divergent ulaG and ulaABCDEF Operons Involved in L-Ascorbate Dissimilation in Escherichia coli

Evangelina Campos, Laura Baldoma, Juan Aguilar,* and Josefa Badia

Department of Biochemistry, Faculty of Pharmacy, University of Barcelona, 08028 Barcelona, Spain

Received 17 November 2003/ Accepted 25 November 2003

The ula regulon, responsible for the utilization of L-ascorbate in Escherichia coli, is formed by two divergently transcribed operons, ulaG and ulaABCDEF. The regulon is negatively regulated by a repressor of the DeoR family which is encoded by the constitutive gene ulaR located downstream of ulaG. Full repression of the ula regulon requires simultaneous interaction of the repressor with both divergent promoters and seems to be dependent on repressor-mediated DNA loop formation, which is helped by the action of integration host factor. Two operator sites have been identified in each promoter. Lack of either of the two sets of operators partially relieved the repression of the other operon; thus, each promoter is dependent on the UlaR operator sites of the other promoter to enhance repression. Electrophoretic mobility shift assays with purified UlaR protein and promoter deletion analyses revealed a conserved sequence, present in each of the four operators, acting as a UlaR binding site. Glucose represses the ula regulon via at least two mechanisms, one dependent on cyclic AMP (cAMP)-cAMP receptor protein (CRP) and the other (possibly inducer exclusion) independent of it. Glucose effects mediated by other global regulators cannot be ruled out with the present information. Changes in cAMP-CRP levels affected only the expression of the ulaABCDEF operon.

* Corresponding author. Mailing address: Departamento de Bioquímica, Facultad de Farmacia, Universidad de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain. Phone: 34-93-403 4496. Fax: 34-93-402 4520. E-mail: jaguilar{at}farmacia.far.ub.es.

Journal of Bacteriology, March 2004, p. 1720-1728, Vol. 186, No. 6
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.6.1720-1728.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Shi, R., Pineda, M., Ajamian, E., Cui, Q., Matte, A., Cygler, M. (2008). Structure of L-Xylulose-5-Phosphate 3-Epimerase (UlaE) from the Anaerobic L-Ascorbate Utilization Pathway of Escherichia coli: Identification of a Novel Phosphate Binding Motif within a TIM Barrel Fold. J. Bacteriol. 190: 8137-8144 [Abstract] [Full Text]  
  • Campos, E., de la Riva, L., Garces, F., Gimenez, R., Aguilar, J., Baldoma, L., Badia, J. (2008). The yiaKLX1X2PQRS and ulaABCDEFG Gene Systems Are Required for the Aerobic Utilization of L-Ascorbate in Klebsiella pneumoniae Strain 13882 with L-Ascorbate-6-Phosphate as the Inducer. J. Bacteriol. 190: 6615-6624 [Abstract] [Full Text]  
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