Escherichia coli K-12 tolF mutants: alterations in protein composition of the outer membrane.

Outer membrane materials prepared from three independently isolated spontaneous Escherichia coli tolF mutants contained no detectable protein Ia. The loss of this protein was nearly completely compensated for by an increase in other major outer membrane proteins, Ib and II. Thus, the major outer membrane proteins accounted for 40% of the total cell envelope protein in both tol+ and tolF strains. No changes were found in the levels of inner membrane proteins prepared from tolF strains when compared with similar preparations from the tol+ strain. Phage-resistant mutants were selected starting with a tolF strain by using either phage TuIb or phage PA2. These phage-resistant tolF strains contained neither protein Ia nor protein Ib. The mutation leading to the loss of protein Ib in these strains is independent of the tolF mutation and is located near malP on the E. coli genetic map.