Genetic and biochemical characterization of an Escherichia coli K-12 mutant with an altered outer membrane protein.

The properties of an Escherichia coli K-12 mutant are described which seemingly produces a "new" major outer membrane protein with an apparent molecular weight of 40 000. This 40K protein was purified and its cyanogen bromide (CNBr) fragments were compared with those of several known major outer membrane proteins. A similarity was found between the CNBr fragments of the 40K protein and those of the OmpF protein (molecular weight 37 000). In addition, the 40K protein was found to be regulated exactly like the OmpF protein, and the mutation which causes the production of the 40K protein has been localized in (or very close to) the ompF gene. It is concluded that the 40K protein is a mutant form of the OmpF protein. The results provide additional evidence that the ompF gene at minute 21 is the structural gene for the OmpF protein.