The arabinose-inducible P(BAD) promoter suffers from all-or-none gene expression in which cells harboring the natively controlled arabinose transport gene (araE) are either induced or uninduced, the relative fraction of which is controlled by the concentration of arabinose. The population-averaged variation in expression from P(BAD) as a function of inducer concentration is proportional to the percentage of cells that are fully induced (vs. uninduced) rather than the level of expression in individual cells. Because of its undesirable effects on the expression of heterologous genes, the all-or-none phenomenon was eliminated in Escherichia coli by expression of araE from arabinose-independent (either the Lactococcus lactis constitutive or IPTG-inducible lac) promoters. In these arabinose-transport engineered cells, variation in P(BAD) expression with arabinose concentration was a result of variation of the expression level in individual cells with all cells in the population having approximately the same induction level.
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