title: Elements involved in catabolite repression and substrate induction of the lactose operon in Lactobacillus casei.
abstract: 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 lacpDeltaRAT 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.
authors.affiliation: Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de Alimentos, 46100 Burjassot, Valencia, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gosalbes
authors.forename: V
authors.initials: V
authors.lastname: Monedero
authors.forename: G
authors.initials: G
authors.lastname: Pérez-Martínez
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D004790:Enzyme Induction; D004794:Enzyme Repression; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D005947:Glucose / Q000494:pharmacology; D005966:Glucuronidase / Q000096:biosynthesis / Q000235:genetics; D006026:Glycoside Hydrolases; D007763:Lac Operon; D007780:Lacticaseibacillus casei / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D007785:Lactose / Q000494:pharmacology; D016296:Mutagenesis; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C064872:antiterminator proteins, Bacteria; C069286:catabolite control proteins, bacteria; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C029022:phosphoenolpyruvate-lactose dependent phosphotransferase system; C037992:phosphoenolpyruvate-mannose phosphotransferase; D006026:Glycoside Hydrolases; D001616:beta-Galactosidase; D005966:Glucuronidase; C022361:6-phospho-beta-galactosidase; D005947:Glucose; D007785:Lactose