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The temperature-dependent expression of OmpF and OmpC, the major channel-forming proteins of the Escherichia coli K-12 outer membrane, was studied. In wild-type cells, decreasing growth temperatures resulted in increased amounts of OmpF protein and correspondingly decreased quantities of OmpC protein. Bacteria deleted for the 13-min chromosomal region did not exhibit this temperature-dependent fluctuation in porin proteins. Plasmid pML22, which consists of pBR322 containing a 0.5-megadalton E. coli chromosomal DNA insert, complemented the thermoregulatory defect. The regulatory gene was named envY. In minicells, pML22 directed the synthesis of an envelope polypeptide (EnvY) having an apparent molecular weight of 25,000. The EnvY protein was synthesized in minicells in greater amounts at 27 degrees C than at 37 degrees C, and a reducing agent was necessary in the solubilization buffer for its subsequent detection on polyacrylamide gels. The results describe the initial characterization of a regulatory system which, along with proteins of the ompB operon, the cyclic AMP system, and the tolC gene product, is involved in a complex network affecting major porin expression.

Gene envY of Escherichia coli K-12 affects thermoregulation of major porin expression