Conjugation-deficient mutants of Escherichia coli distinguish classes of functions of the outer membrane OmpA protein.

Sixty-two E. coli mutants, selected as being deficient as recipients in F factor conjugation, are altered either in the amount or function of the outer membrane OmpA protein or in lipopolysaccharide structure. These two components may function together in conjugation, since the residual conjugation activity of a mutant lacking OmpA protein was unaffected by the additional presence of a lipopolysaccharide defect. Sixty of the strains carried mutations mapping to ompA, and these could be divided into classes depending on the amount of OmpA protein in their membranes. Representatives of these classes of mutant alleles failed to complement in diploids, indicating that they all affect the ompA structural gene and nearby sequences needed for its expression. The properties of these classes distinguish three groups of OmpA protein functions: 1) the structural function in the outer membrane in providing resistance to chelating agents and the hydrophobic antibiotic novobiocin, 2) the receptor functions in phage TuII and K3 infection, and 3) the functions of binding cells together during conjugation, facilitating the uptake of receptor-bound colicin K or L, and allowing phage Ox2 to infect. Different cellular amounts or sites in OmpA protein are thus required for these three groups of functions.