Mutations in genes cpxA and cpxB alter the protein composition of Escherichia coli inner and outer membranes

Abstract

Mutations in chromosomal genes cpxA and cpxB altered the protein composition of the inner and outer bacterial membranes. Electrophoretic analyses of membrane proteins from isogenic strains differing only at their cpx loci and of spontaneous cpxA+ revertants of a cpxA cpxB double mutant showed that the alterations define a pattern that is uniquely attributable to the cpx mutations. Two major outer membrane proteins, the OmpF matrix porin and the murein lipoprotein, were deficient or absent from the outer membrane of mutant cells, whereas the quantities of two other major outer membrane proteins, the OmpC matrix porin and the OmpA protein, were not significantly altered. The cpx mutations did not generally alter the functional or chemical properties of the cell envelope. In the electron microscope, mutant cells appeared ovoid, but individual cells showed no surface irregularities to suggest gross defects in the cell envelope. These observations suggest that the primary effect of the mutations is to alter selectively the synthesis or translocation of certain envelope proteins.