Genetically structured models for lac promoter-operator function in the chromosome and in multicopy plasmids: Lac promoter function.

A mathematical model based on molecular mechanisms for regulation of the lactose (lac) operon in Escherichia coli has been extended and applied to investigate the lac promoter function in the chromosome and in multicopy plasmids. The model simulates the influence of certain host cell mutations and also mutations in the lac promoter sequence in the chromosome in reasonable agreement with previous experimental measurements. The effect of the plasmid copy number and the cloning vector size on the promoter function of a cloned lac regulatory sequence in multicopy plasmids has also been examined. Model results indicate that the efficiency of the cloned lac promoter function is significantly decreased as the number of promoters per cloning vector and size of the vector are increased. The simulation results predict a maximum in the cloned gene transcription rate with respect to the plasmid copy number.