LAUSR

Significance It is well established that certain intracellular regulators can stabilize DNA loops to greatly enhance activation or repression of gene transcription. In vitro and in vivo ensemble measurements have determined that only a few copies of regulators are, in fact, needed to stably form DNA loops. In view of such a small number, we address the issue of sensitivity of gene regulation by DNA looping to variations of intracellular parameters in individual growing Escherichia coli bacteria. Surprisingly, we find that DNA looping from the lac system is robust to a range of perturbations, including divisions during which cells can maintain tight repression over many generations. We propose molecular hypotheses compatible with the observed robustness across a range of intracellular perturbations.