title: Effector Overlap between thelacandmelOperons of Escherichia coli: Induction of themelOperon with β-Galactosides.
abstract: Thelac(lactose) operon (which processes β-galactosides) and themel(melibiose) operon (which processes α-galactosides) ofEscherichia colihave a close historical connection. A number of shared substrates and effectors of the permeases and regulatory proteins have been reported over the years. Until now, β-thiogalactosides like TMG (methyl-β-d-thiogalactopyranoside) and IPTG (isopropyl-β-d-thiogalactopyranoside) have not generally been considered to be inducers of themeloperon. The same is true for β-galactosides such as lactose [β-d-galactopyranosyl-(1→4)-d-glucose], which is a substrate but is not itself an inducer of thelacoperon. This report shows that all three sugars can induce themeloperon significantly when they are accumulated in the cell by Lac permease. Strong induction by β-thiogalactosides is observed in the presence of Lac permease, and strong induction by lactose (more than 200-fold) is observed in the absence of β-galactosidase. This finding calls for reevaluation of TMG uptake experiments as assays for Lac permease that were performed withmel+strains.IMPORTANCEThe typical textbook picture of bacterial operons is that of stand-alone units of genetic information that perform, in a regulated manner, well-defined cellular functions. Less attention is given to the extensive interactions that can be found between operons. Well-described examples of such interactions are the effector molecules shared by thelacandmeloperons. Here, we show that this set has to be extended to include β-galactosides, which have been, until now, considered not to effect the expression of themeloperon. That they can be inducers of themeloperon as well as thelacoperon has not been noted in decades of research because of theEscherichia coligenetic background used in previous studies.
authors.affiliation: Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India.
authors.forename: Atul
authors.initials: A
authors.lastname: Narang
authors.affiliation: Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India soehler@dbeb.iitd.ac.in.
authors.forename: Stefan
authors.initials: S
authors.lastname: Oehler
mesh_terms: D004926:Escherichia coli / Q000235:genetics*; D005697:Galactosides / Q000235:genetics / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007763:Lac Operon; D007785:Lactose / Q000494:pharmacology; D008553:Melibiose / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins; D009876:Operon; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D005697:Galactosides; D026901:Membrane Transport Proteins; C007816:beta-galactoside; C021499:lactose permease; D008553:Melibiose; D001616:beta-Galactosidase; D005947:Glucose; D007785:Lactose
keywords: beta-galactosides; coactivator; inducer; lac operon; mel operon