Regulation of lac operon expression in mixed sugar chemostat cultures

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Abstract
Expression of the lactose (lac) operon in the Escherichia coli chromosome has been studied in mixed-sugar chemostat cultures under steady-state and transient conditions. A unified model has been formulated which involves regulation of active inducer (lactose) transport, promoter–operator regulated expression of the lac operon, glucose-mediated inducer exclusion, and catabolite repression. The model of the lac operon control system focuses on the molecular interactions among the regulatory species and the genetic control elements for the initiation of transcription. The role of catabolite modulator factor (CMF) in the regulation of transcription is described. The modeling of glucose-mediated regulation of intracellular cyclic adenosine monophosphate (cAMP) and inducer exclusion is based on the recently elucidated mechanisms of the involvement of the PTS (phosphoen-olpyruvate dependent sugar transport system) enzymes, in the presence of glucose, in regulation of adenylate cyclase and non-PTS sugar transport proteins (i.e. per-meases). The adequacy of the unified model was verified with experimental data.