Fig. 3.

Most inactive ExbB mutants are dominant. (A) Expression of plasmid-encoded ExbB mutants and ExbD was fully induced with 0.2% l-arabinose in the wild-type strain W3110 1 h prior to an assay of the iron transport. Immediately prior to the transport assays samples were precipitated with TCA. Dilutions of equal A₅₅₀-ml samples were electrophoresed on 13% SDS-polyacrylamide gels and immunoblotted with anti-ExbB antibody to determine relative levels of overexpression. The identities of the ExbB variants and the dilutions are indicated above the lanes. The positions of ExbB monomer, ExbB(Δ195-243), and the proteolytic degradation products are noted on the right. Mass standards are indicated on the left. The figure is a composite of two immunoblots. (B) Initial rates of iron transport were determined multiple times in triplicate assays after 1 h of induction with 0.2% l-arabinose. Averages are shown as a percentage of W3110 from which plasmid-encoded ExbB(C25A) and ExbD (pKP878) were overexpressed. The standard deviations are indicated on each bar.