We are studying various aspects of the DNA-binding of the Escherichia coli proteins, HU-A and HU-B. In doing so, we have generated fluorescent protein-tagged versions of HU, using red fluorescent protein (RFP) and also a yellow fluorescent protein (Venus). In this paper, we show that individual cells in a population of identical cells with identical genetic backgrounds, all of which are overexpressing these proteins, show considerable cell-to-cell variations in levels of expression, as well as leaky expression even under conditions of non-induction by IPTG. We show that this technique of visualizing the fluorescent-protein tagged HU (which illuminates the bacterial nucleoid) is ideal for examining leaky expression as well as cell-to-cell variations in expression of any protein tagged to the fluorescent protein.

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