LptD is degraded by different proteases at discrete points in the assembly process. Relative OMP levels were determined from whole-cell lysates in wild-type strains, i.e., NR754 (A), GC169 (B), or HC340 (C), and strains containing each of the chromosomal mutations listed, in a lptD4213 (A), lptE6 (B), or lptDY721D (C) background by SDS-PAGE and immunoblotting for the proteins indicated. Red, reduced; Ox, oxidized.