PMID:16432263

Citation	Oehler, S, Alberti, S and Müller-Hill, B (2006) Induction of the lac promoter in the absence of DNA loops and the stoichiometry of induction. Nucleic Acids Res. 34:606-12
Abstract	In vivo induction of the Escherichia coli lactose operon as a function of inducer concentration generates a sigmoidal curve, indicating a non-linear response. Suggested explanations for this dependence include a 2:1 inducer-repressor stoichiometry of induction, which is the currently accepted view. It is, however, known for decades that, in vitro, operator binding as a function of inducer concentration is not sigmoidal. This discrepancy between in vivo and in vitro data has so far not been resolved. We demonstrate that the in vivo non-linearity of induction is due to cooperative repression of the wild-type lac operon through DNA loop formation. In the absence of DNA loops, in vivo induction curves are hyperbolic. In the light of this result, we re-address the question of functional molecular inducer-repressor stoichiometry in induction of the lac operon.
Links	PubMed PMC1345695 Online version:10.1093/nar/gkj453
Keywords	DNA, Bacterial/chemistry; Escherichia coli/genetics; Gene Expression Regulation, Bacterial; Lac Operon; Models, Genetic; Nucleic Acid Conformation; Operator Regions, Genetic; Promoter Regions, Genetic; Repressor Proteins/metabolism; Transcriptional Activation
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