A suppressor mutation that creates a faster and more robust σE envelope stress response

The σE envelope stress response is an essential signal transduction pathway which detects and removes mistargeted outer membrane (OM) β-barrel proteins (OMPs) in the periplasm of Escherichia coli. It relies on σE, an alternative sigma factor encoded by the rpoE gene. Here we report a novel mutation, a nucleotide change of C to A in the third base of the second codon, which increases levels of σE (rpoE_S2R). The rpoE_S2R mutation does not lead to the induction of the stress response during normal growth but instead changes the dynamics of induction upon periplasmic stress, resulting in a faster and more robust response. This allows cells to adapt faster to the periplasmic stress, avoiding lethal accumulation of unfolded OMPs in the periplasm caused by severe defects in the OMP assembly pathway.