FIG. 3.

Solid-phase Tf binding assay. Equal amounts of iron-depleted whole cells from the parental and mutant Tbp derivatives were dotted onto nitrocellulose. The blots were incubated with biotinylated human holotransferrin and developed by using horseradish peroxidase-streptavidin to detect Tf binding. TbpA⁺B⁺, 7169; TbpA⁺B⁻, 7169b12; TbpA⁻B⁺, 7169tbpA35; TbpA⁻B⁻, 7169tbpAB-1.