The LysR homolog LrhA promotes RpoS degradation by modulating activity of the response regulator sprE

Synthesis of the OmpF porin of Escherichia coli is regulated in response to environmental and growth phase signals. In order to identify constituents of the various regulatory pathways involved in modulating ompF transcriptional expression, transposon insertion mutagenesis was performed and mutations that increased ompF*-lacZ activity were identified as previously described. Mutations mapping to a previously identified gene of unknown function, lrhA, were obtained. We found that LrhA, a LysR homolog, functions as a regulatory component in the RpoS-dependent growth phase repression of ompF. In addition to altered growth phase regulation of ompF, these lrhA mutants have pleiotropic stationary-phase defects as a result of decreased RpoS levels. We provide evidence that LrhA promotes degradation of RpoS by functioning within a genetic pathway that includes the response regulator SprE and the ClpXP protease. LrhA functions upstream of the other components in the pathway and appears to modulate the activity of SprE. Physiological adaptation to changing environmental condi-tions is essential to microbial viability. This is particularly im-portant for bacteria that alternatively inhabit distinct niches differing in conditions of oxidative stress, temperature, pH, and osmolarity, as well as nutrient availability and exposure t