Osmoregulation of gene expression. I. DNA sequence of the ompR gene of the ompB operon of Escherichia coli and characterization of its gene product.

The ompB region on the Escherichia coli chromosome codes for two genes, ompR and envZ, which are required for the osmolarity sensitive biosynthetic regulation of the outer membrane matrix proteins (porins), OmpF and ompC. A part of the ompB region containing the ompR gene has been cloned (Wurtzel, E. T., Movva, N. R., Ross, F. L., and Inouye, M. (1981) J. Mol. Appl. Genet. 1, 61-69). We have determined the DNA sequence, including the promoter and structural regions encompassed in a 1.3-kilobase pair Ava I-Eco RI subfragment. This fragment codes for the entire ompR gene as well as the 5' end of the envZ gene. The ompR gene codes for a protein of 32,489 daltons, consisting of 284 amino acid residues. This was confirmed by identifying the gene product by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and determining a partial amino acid sequence of the NH2-terminal region of the gene product. A sequence of 57 amino acid residues located in the COOH-terminal region of the protein is extremely basic. It contains 10 arginine plus lysine residues in contrast to 1 glutamic acid residue in this region. In vitro transcription of the DNA from this region indicates that ampR and envZ are co-transcribed as a polycistronic mRNA from a promoter located 5' to the ompR gene. Translation of the am pR gene terminates at two tandem TAS codons and translation of the envZ gene initiates 29 nucleotides downstream. Cloning of the promoter region of ompB at a site 5' to the structural portion of the beta-galactosidase gene indicates that transcription of ompB is under positive control by cAMP.