Suppressor mutations in rpoA suggest that OmpR controls transcription by direct interaction with the α subunit of RNA polymerase

We have isolated mutations in rpoA, the gene encoding the α subunit of RNA polymerase, that specifically affect transcriptional control by OmpR and EnvZ, the two-component regulatory system that controls porin gene expression in Escherichia coli. Characterization of these mutations and a previously isolated rpoA allele suggests that both positive and negative regulation of porin gene transcription involves a direct interaction between OmpR and RNA polymerase through the α subunit. Several of the rpoA mutations cluster in the carboxy-terminal portion of the α protein, further suggesting that it is this domain of α that is involved in interaction with OmpR and perhaps other transcriptional regulators as well.