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Journal of Bacteriology, July 1999, p. 3928-3934, Vol. 181, No. 13
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Elements Involved in Catabolite Repression and Substrate Induction of the Lactose Operon in Lactobacillus casei

María José Gosalbes, Vicente Monedero, and Gaspar Pérez-Martínez*

Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de Alimentos, 46100 Burjassot, Valencia, Spain

Received 28 December 1998/Accepted 19 April 1999

In Lactobacillus casei ATCC 393, the chromosomally encoded lactose operon, lacTEGF, encodes an antiterminator protein (LacT), lactose-specific phosphoenolpyruvate-dependent phosphotransferase system (PTS) elements (LacE and LacF), and a phospho-beta -galactosidase. lacT, lacE, and lacF mutant strains were constructed by double crossover. The lacT strain displayed constitutive termination at a ribonucleic antiterminator (RAT) site, whereas lacE and lacF mutants showed an inducer-independent antiterminator activity, as shown analysis of enzyme activity obtained from transcriptional fusions of lac promoter (lacp) and lacpDelta RAT with the Escherichia coli gusA gene in the different lac mutants. These results strongly suggest that in vivo under noninducing conditions, the lactose-specific PTS elements negatively modulate LacT activity. Northern blot analysis detected a 100-nucleotide transcript starting at the transcription start site and ending a consensus RAT sequence and terminator region. In a ccpA mutant, transcription initiation was derepressed but no elongation through the terminator was observed in the presence of glucose and the inducing sugar, lactose. Full expression of lacTEGF was found only in a man ccpA double mutant, indicating that PTS elements are involved in the CcpA-independent catabolite repression mechanism probably via LacT.

* Corresponding author. Mailing address: Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de los Alimentos (CSIC), Polígono de la Coma s/n, Apartado de correos 73, 46100 Burjassot, Valencia, Spain. Phone: 34 96 3900022. Fax: 34 96 3636301. E-mail: gaspar.perez{at}iata.csic.es.

Journal of Bacteriology, July 1999, p. 3928-3934, Vol. 181, No. 13
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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